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Mollusca
Fossil range: Cambrian–Recent
Tonicella lineata, a polyplacophoran or chiton, anterior end towards the right
Scientific classification
Kingdom: Animalia
Superphylum: Lophotrochozoa
Phylum: Mollusca
Linnaeus, 1758
Classes
Diversity
85,000[1] recognized living species
Molluscs[note 1] belong to the animal phylum Mollusca. There are around 85,000 recognized extant species, making it the largest marine phylum as it contains about 23% of named marine organisms. Representatives live in marine, freshwater, and terrestrial habitats. Molluscs are highly diverse in size, in anatomical structure, in behaviour and in habitat.
.The phylum is typically divided into nine or ten taxonomic classes, of which two are extinct.^ Circulatory - Mammal circulatory systems are divided into two circuits: pulmonary and systemic.
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^ Nevertheless, they can be divided into two groups on the basis of embryological evidence (Figure 09).
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The gastropods (snails and slugs) include by far the most classified species, accounting for 80% of the total. .Cephalopod molluscs such as squid, cuttlefish and octopus are among the most neurologically advanced invertebrates.^ Cephalopods such as cuttlefish, squid and octopuses have eyes that are similar to those of vertebrates like humans (with small variation in the orientation of the retinal cells).
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^ Ns2: Nesis, K.N. 1987 (Translation by B.S. Levitov of original Russion version of 1982): Cephalopods of the World: Squids, Cuttlefishes, Octopuses, and Allies.

Either the giant squid or the colossal squid is the largest known invertebrate species.
Molluscs have diverse body structures. .The two most universal characteristics are a mantle with a significant cavity used for breathing and excretion, and the structure of the nervous system.^ Food particles and water enter the mantle cavity by way of the incurrent siphon (Figure 10), a posterior opening between the two valves.
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^ Both systems use chemical signals to bring about a desired response in some target, perhaps a muscle (in the case of the nervous system) or the liver (in the case of the endocrine system).
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^ The mantle cavity is the space between the two folds of the mantle.
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.As a result, many textbooks base their descriptions on a hypothetical "generalized mollusc", with features common to many, but not all species.^ Sy2: Sysoev, A.V.; Kantor, Y.I. 1989: Anatomy of molluscs of genus Splendrillia with descriptions of two new bathyal species of the genus from New Zealand.

^ Haa1: Haase, M. 2008: The radiation of hydrobiid gastropods in New Zealand: a revision including the description of new species based on morphology and mtDNA sequence information.

.There is good evidence for the appearance of gastropods, cephalopods and bivalves in the Cambrian period 542 to 488.3 million years ago.^ All phyla of animals had evolved by the beginning of the Paleozoic Era some 540 million years ago.
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^ Ba1: Brook, F.J.; Marshall, B.A. 1998: Appendix: Checklist of benthic coastal marine chitons, bivalves, gastropods and cephalopods of the northern Kermadec Islands.

^ The human lineage split from that of the apes occurred about 5 - 10 million years ago in Africa.
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.However, the evolutionary history both of molluscs' emergence from the ancestral Lophotrochozoa and of their diversification into the well-known living and fossil forms are still vigorously debated.^ Wd3: Williams, S.T. 2007: Origins and diversification of Indo-West Pacific marine fauna: evolutionary history and biogeography of turban shells (Gastropoda, Turbinidae).

There is a risk of food-poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations that aim to minimize this risk. Molluscs have for centuries also been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye, and sea silk. Their shells have also been used as money in some pre-industrial societies.
Mollusc species can also present as hazards or pests to humans. Blue-ringed octopus bites are often fatal, and Octopus apollyon bites can cause inflammation that lasts longer than one month. Stings from a few species of large tropical cone shells can also kill. Their sophisticated though easily-produced venoms have also become important tools in neurological research. .Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is transmitted to humans via water snail hosts, and affects about 200 million people.^ The human lineage split from that of the apes occurred about 5 - 10 million years ago in Africa.
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^ Human diving experience indicates that sound wave in water can only be perceived through bone conductivity via vibration of the bones of the skull.
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.Snails and slugs can also be serious agricultural pests, and accidental or deliberate introduction of snail species into new environments has seriously damaged some ecosystems.^ Hy1: Harry, H.W. 1967: A review of the living tectibranch snails of the genus Volvulella , with descriptions of a new subgenus and species from Texas.

^ Mr24: Marshall, B.A. 1993: The systematic position of Larochea Finlay, 1927, and introduction of a new genus and two new species (Gastropoda: Scissurellidae).

^ Cl8: Climo, F.M. 1979: The systematic status of some land snails mistakenly assigned to the New Zealand fauna.

Contents

Diversity

About 80% of all known mollusc species are gastropods.[2]
.Estimates of accepted described living species of molluscs vary from 50,000 to maximum 120,000 species.^ Fl1: Fleming, C.A. 1978: The bivalve genus Limatula : a list of described species and a review of living and fossil species in the Southwest Pacific.

[1] .In 2009 Chapman estimated described living 85,000 species.^ Fl1: Fleming, C.A. 1978: The bivalve genus Limatula : a list of described species and a review of living and fossil species in the Southwest Pacific.

[1] Haszprunar in 2001 estimated about 93,000 named species,[3] which include 23% of all named marine organisms.[4] .Molluscs are second only to arthropods in numbers of living animal species[2] – far behind the arthropods' 1,113,000 but well ahead of chordates' 52,000.[5] It has been estimated that there are about 200,000 living species in total,[6][1] and 70,000 fossil species,[7] although the total number of mollusc species that ever existed, whether or not preserved, must be many times greater than the number alive today.^ It is not accidental that the full apparatus of ear developed only after animals making a living on land.
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^ Since insects comprise one of the largest animal groups - both in number of species (about 1 million) and in number of individuals, the grasshopper will be used as the anatomical example (Figure 16e), also see a crayfish anatomy in Figure 16b.
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^ The handle must have a length equal to or greater than 150 percent of the vessel's freeboard or 6 ft (1.83 m), whichever is greater.
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[8]
.Molluscs have more varied forms than any other animal phylumsnails and other gastropods, clams and other bivalves, squids and other cephalopods, and other lesser-known but similarly distinctive sub-groups.^ Ba1: Brook, F.J.; Marshall, B.A. 1998: Appendix: Checklist of benthic coastal marine chitons, bivalves, gastropods and cephalopods of the northern Kermadec Islands.

^ Widespread polyphyly among Alopiinae snail genera: when phylogeny mirrors biogeography more closely than morphology.
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^ Other longline vessels with freeboards of more than 3 ft (0.91m).
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The majority of species still live in the oceans, from the seashores to the abyssal zone, but some are significant members of freshwater and terrestrial ecosystems. .They are extremely diverse in tropical and temperate regions but can be found at all latitudes.^ Thus, their cellular defense systems are extremely sensitive, and they respond rapidly to minor perturbations, all without any specific adaptive capabilities.
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[9] .About 80% of all known mollusc species are gastropods.^ About 80% of all known mollusc species are gastropods.
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^ Back to top ] About 80% of all known mollusc species are gastropods .
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^ About 6,000 species — all of them marine.
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[2] Cephalopoda such as squid, cuttlefish and octopus are among the most neurologically-advanced of all invertebrates.[10] .The giant squid, which until recently had not been observed alive in its adult form,[11] is one of the largest invertebrates.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ The zygote develops into a swimming larva that can fend for itself until it develops into the adult form.
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However a recently-caught specimen of the colossal squid, 10 metres (33 ft) long and weighing 500 kilograms (0.49 LT; 0.55 ST), may have overtaken it.[12]
Freshwater and terrestrial molluscs appear exceptionally vulnerable to extinction. .Estimates of the numbers of non-marine molluscs vary widely, partly because many regions have not been thoroughly surveyed and there is a shortage of specialists in classifying these animals.^ If two or more owners have the same number of points and there are insufficient permits for all such owners, the Regional Administrator shall issue the permits through a lottery.
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^ Fisheries and research data from many of these species have been analyzed by regional management agencies.
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^ The division of the body into distinct areas seems to have allowed diversification to occur because there are many different types of mollusks adapted to various ways of life.
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.However, in 2004 the IUCN Red List of Threatened Species included nearly 2,000 endangered non-marine molluscs.^ Non-precious coral means any species of coral other than those listed under the definitions for precious coral in Sec.
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^ If the Regional Administrator determines that a change in the size of the study zones would not result in fishing for bottomfish in the NWHI that would adversely affect any species listed as threatened or endangered under the ESA. (b) After consulting with the Council.
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^ CFR CHAPTER II PART 223--THREATENED MARINE AND ANADROMOUS SPECIES 0 4.
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.For comparison, the great majority of molluscs species are marine but only 41 of these appeared on the 2004 Red List.^ These worms, which are generally colorless and less than 5 cm long, occur almost anywhere and in great variety (15000 known species).
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42% of recorded extinctions since 1500 involved molluscs, almost entirely non-marine.[13]

Definition

.The word mollusc is derived from the French mollusque, which originated from the Latin molluscus, from mollis, soft.^ The name of the phylum is derived from Latin word molluscus meaning soft.

^ The word "mollusc" or "mollusk" (both are correct) is derived from the Latin word mollis meaning "soft".
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^ The word mollusc is derived from the French mollusque , which originated from the Latin molluscus , from mollis , soft.
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Molluscus was itself an adaptation of Aristotle's τᾲ μαλάκια, "the soft things", which he applied to cuttlefish.[14] The scientific study of molluscs is known as malacology.[15]
Molluscs have developed such a varied range of body structures that it is difficult to find synapomorphies (defining characteristics) that apply to all modern groups.[9] The following are present in all modern molluscs:[5][7]
Other characteristics that commonly appear in textbooks have significant exceptions:
  Class
Characteristic[7] Aplacophora[5]:291–292 Polyplacophora[5]:292–298 Monoplacophora[5]:298–300 Gastropoda[16] Cephalopoda[17] Bivalvia[18] Scaphopoda[19]
Radula, a rasping "tongue" with chitinous teeth Absent in 20% of Neomeniomorpha Yes Yes Yes Yes No Internal, cannot extend beyond body
Broad, muscular foot Reduced or absent Yes Yes Yes Modified into arms Yes Small, only at "front" end
Dorsal concentration of internal organs (visceral mass) Not obvious Yes Yes Yes Yes Yes Yes
Large digestive ceca No ceca in some aplacophora Yes Yes Yes Yes Yes No
Large complex metanephridia ("kidneys") None Yes Yes Yes Yes Yes Small, simple

A "generalized mollusc"

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    Digestive & excretory system
    Circulatory & respiratory
    Central nervous system
    Reproductive system
 1 Radula
 2 Mouth
 3 Shell
 4 Stomach
 5 Gonad
 6 Heart
 7 Coelom
 9 Mantle
10 Mantle cavity
11 Anus
12 Gill
13 Foot
15 Pedal nerve cord
16 Gut
17 Visceral nerve cord
18 Nerve ring
A generalized mollusc[20]
.Because of the enormous variations between groups of molluscs, many text books start the subject by describing a "generalized mollusc", which some suggest may resemble very early molluscs and which is rather similar to modern monoplacophorans.^ Comparing gene sequences (with other animals) suggests that they may be very close to the "Animal Eve" called urmetazoan .
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^ Recognition between sperm and egg may involve the acrosomal process for some species.
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^ Mollusks are a very large and diversified group containing many thousands of living and extinct forms.
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[9][21][22][23]
The generalized mollusc has a single, "limpet-like" shell on top. .The shell is secreted by a mantle that covers the upper surface.^ The mantle may secrete a shell.
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^ Musculo-skeletal - In a clam, the shell is secreted by the mantle and is composed of calcium carbonate with an inner layer of mother-of-pearl .
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The underside consists of a single muscular "foot".[21]

Mantle and mantle cavity

.The mantle cavity is a fold in the mantle that encloses a significant amount of space.^ The mantle cavity is the space between the two folds of the mantle.
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The cavity was probably at the rear in the earliest molluscs but its position now varies from group to group. .The anus, a pair of osphradia (chemical sensors) in the incoming "lane", the hindmost pair of gills and the exit openings of the nephridia ("kidneys") and gonads (reproductive organs) are in the mantle cavity.^ The nephridia empty into the mantle cavity.
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^ Food particles and water enter the mantle cavity by way of the incurrent siphon (Figure 10), a posterior opening between the two valves.
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^ Nephridia have two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall.
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[21]

Shell

.The mantle secretes a shell that is mainly chitin and conchiolin (a protein) hardened with calcium carbonate,[21][24] except that the outermost layer is all conchiolin.^ The mantle may secrete a shell.
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^ Protein matrix lined with calcium carbonate .
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^ Musculo-skeletal - In a clam, the shell is secreted by the mantle and is composed of calcium carbonate with an inner layer of mother-of-pearl .
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[21] Molluscs never use phosphate to construct their hard parts,[25] with the questionable exception of Cobcrephora.[26]

Foot

The underside consists of a muscular foot, which has adapted to different purposes in different classes.[27]:4 The foot carries a pair of statocysts which act as balance sensors. .In gastropods, it secretes mucus as a lubricant to aid movement.^ In gastropods, it secretes mucus as a lubricant to aid movement.
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^ The underside of the body generally consists of a muscular foot, which secretes mucus as a lubricant to aid movement.
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^ In many gastropods, slippery mucus is secreted from mantle extensions, or parapodia, as a defense against larger predators, such as sea stars (starfish).
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.In forms that have only a top shell, such as limpets, the foot acts as a sucker attaching the animal to a hard surface, and the vertical muscles clamp the shell down over it; in other molluscs, the vertical muscles pull the foot and other exposed soft parts into the shell.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ Reptiles with limbs, such as lizards, are able to lift their body off the ground, and the body is covered with hard, horny scales that protect the animal from desication and from predators.
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^ In higher vertebrates, other parts of the skeleton serve as attachment for muscles and for protection of internal organs of the thoracic cavity and the abdomen.
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[21] .In bivalves, the foot is adapted for burrowing into the sediment;[27]:4 in cephalopods it is used for jet propulsion,[27]:4 and the tentacles and arms are derived from the foot.^ In cephalopods ("head-footed"), such as octopuses, the foot has evolved into tentacles about the head.
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[28]

Multiple functions of organs

Molluscs organs are used for multiple functions. .For example: the heart and nephridia ("kidneys") are important parts of the reproductive system as well as the circulatory and excretory systems; in bivalves, the gills both "breathe" and produce a water current in the mantle cavity which serves both excretion and reproduction.^ The nephridia empty into the mantle cavity.
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^ Wastes from the digestive gland tubules are returned to the stomach and are eventually swept into the intestine Excretory - There are two excretory kidneys in the clam (Figure 10), which lie just below the heart and remove waste from the pericardial cavity for excretion into the mantle cavity.
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^ Excretory - The kidneys are important excretory and water-regulating organs that conserve or rid the body of water as appropriate.
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Circulation

.Molluscs' circulatory systems are mainly open.^ Circulatory - They have an open circulatory system.
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^ Such a circulatory system is called an open circulatory system because the blood is not contained within blood vessels all the time.
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Although molluscs are coelomates, their coeloms are reduced to fairly small spaces enclosing the heart and gonads. .The main body cavity is a hemocoel through which blood circulates and which encloses most of the other internal organs.^ Other special joints allow a cat to turn its head to reach most parts of its body.
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^ The third heart pumps blood through the rest of the body.
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^ In higher vertebrates, other parts of the skeleton serve as attachment for muscles and for protection of internal organs of the thoracic cavity and the abdomen.
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.The blood contains the respiratory pigment hemocyanin as an oxygen-carrier.^ The systemic circuit carries oxygenated blood to all the body's cells via arteries, and deoxygenated blood back to the heart via veins.
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^ Here oxygen from the air diffuses into the blood, where it is carried by hemoglobin.
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^ The heart pumps blue blood, containing the pigment hemocyanin instead of red hemoglobin, into vessels that lead to the various organs of the body.
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.The heart consists of one or more pairs of atria (auricles) which receive oxygenated blood from the gills and pump it to the ventricle, which pumps it into the aorta (main artery), which is fairly short and opens into the hemocoel.^ One or more renal arteries can be present to receive blood from the renal portal system.
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^ From the hemocoel blood passes into the veins and back to the auricle.
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^ There is a heart at the end of each of their gills; these hearts pump blood through the gills.
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[21]
.The atria of the heart also function as part of the excretory system by filtering waste products out of the blood and dumping it into the coleom as urine.^ Urine is a waste product of the urinary system process while feces are waste products of the digestive system.
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^ The more complex animals have organ systems to carry out these functions; in simple animals, these functions sometimes are carried out by specialized tissues.
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^ Their mantle is richly supplied with blood vessels and functions as a lung when air is moved in and out through respiratory pores (Figure 11).
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.A pair of nephridia ("little kidneys") to the rear of and connected to the coelom extracts any re-usable materials from the urine and dumps additional waste products into it, and then ejects it via tubes that discharge into the mantle cavity.^ The nephridia empty into the mantle cavity.
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^ The anus opens into the mantle cavity near the edge of the mantle and the shell (see Figure 11).
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^ Urine is a waste product of the urinary system process while feces are waste products of the digestive system.
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[21]

Respiration

.Most molluscs have only one pair of gills, or even only one gill.^ Most molluscs have gills.
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^ Most molluscs have only one pair of gills, or even only one gill.
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^ Saltwater pearl oyster farm in Seram, Indonesia Most molluscs that have shells can produce pearls, but only the pearls of bivalves and some gastropods whose shells are lined with nacre are valuable.
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.Generally the gills are rather like feathers in shape, although some species have gills with filaments on only one side.^ Generally the gills are rather like feathers in shape, although some species have gills with filaments on only one side.
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^ All have a single chambered heart, one gill, a penis-like organ for internal fertilization, more complex nerve ganglia, and well structured sensory organs.  .

^ Respiration is usually accomplished with a feather-like gill (ctenidium) that extends into the mantle cavity at the anterior of the body.
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.They divide the mantle cavity so that water enters near the bottom and exits near the top.^ They are bilaterally symmetrical, ovoid shaped and flattened top to bottom; and as their name infers bear eight articulating plates dorsally.

^ Near the base of the ctenidium is a patch of sensory epithelium innervated from the branchial nerve , forming a sense-organ called the osphradium, whose function is to test the water entering the branchial cavity.

^ All cephalopods swim by rapidly expelling water from their mantle cavity.

.Their filaments have three kinds of cilia, one of which drives the water current through the mantle cavity, while the other two help to keep the gills clean.^ Water flows in through one siphon, the incurrent siphon, and passes over a series of gill filaments.
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^ Gastropods (snails) are found in freshwater, and have conquered the land by converting their mantle cavity into a lung (hence their name pulmonate snails) eliminating their primitive gills.

^ They are known to have three or four denticles on their columellar lip and two larger denticles, enclosing five smaller ones, on the outer lip.
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.If the osphradia detect noxious chemicals or possibly sediment entering the mantle cavity, the gills' cilia may stop beating until the unwelcome intrusions have ceased.^ Food particles and water enter the mantle cavity by way of the incurrent siphon (Figure 10), a posterior opening between the two valves.
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^ Respiratory - Within the mantle cavity, the gills (Figure 10) hang down on either .
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.Each gill has an incoming blood vessel connected to the hemocoel and an outgoing one to the heart.^ The heart pumps blue blood, containing the pigment hemocyanin instead of red hemoglobin, into vessels that lead to the various organs of the body.
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^ Hemoglobin-containing blood moves anteriorly in a dorsal blood vessel and then is pumped by five pairs of hearts into a ventral blood vessel.
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^ Circulatory - The heart of a fish is a simple pump, and the blood flows through the chambers, including a nondivided atrium and ventricle, to the gills only.
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[21]

Eating, digestion, and elimination

    = Food
    = Radula
    = Odontophore "belt"
    = Muscles
Snail radula at work.
.Most molluscs have muscular mouths with radulae, "tongues" bearing many rows of chitinous teeth, which are replaced from the rear as they wear out.^ The teeth are fastened to the radula in rows.
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.The radula primarily functions to scrape bacteria and algae off rocks.^ The rock-scraping radula, a striking case of convergence (Mollusca).-- Neth.
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.Molluscs mouths also contain glands that secrete slimy mucus, to which the food sticks.^ Food in the mouth is mixed with saliva, which contains enzymes that begin the process of digestion.
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^ The anterior salivary gland secrets the clear liquid (of water, mucin, protein, and enzymes) into the mouth.
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^ The pedal gland at front end of the foot secretes a thin, flat ribbon of mucus for the snail to move along.
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.Beating cilia (tiny "hairs") drive the mucus towards the stomach, so that the mucus forms a long string.^ Beating cilia (tiny "hairs") drive the mucus towards the stomach, so that the mucus forms a long string.
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^ At the tapered rear end of the stomach and projecting slightly into the hindgut is the prostyle , a backward-pointing cone of feces and mucus, which is rotated by further cilia so that it acts as a bobbin , winding the mucus string onto itself.
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^ Before the mucus string reaches the prostyle the acidity of the stomach makes the mucus less sticky and frees particles from it.
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[21]
At the tapered rear end of the stomach and projecting slightly into the hindgut is the prostyle, a backward-pointing cone of feces and mucus, which is rotated by further cilia so that it acts as a bobbin, winding the mucus string onto itself. Before the mucus string reaches the prostyle, the acidity of the stomach makes the mucus less sticky and frees particles from it.[21]
.The particles are sorted by yet another group of cilia, which send the smaller particles, mainly minerals, to the prostyle so that eventually they are excreted, while the larger ones, mainly food, are sent to the stomach's cecum (a pouch with no other exit) to be digested.^ Mucous secretions cause smaller particles to adhere to the gills, and cilia action sweeps them toward the mouth.
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^ Gastrulation - The cells in the blastula undergo dramatic movements wherein they change their positions relative to one another.
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^ Fish such as bass that are piscivorous (eat other fish) have fairly short intestines because such food is easy to chemically break down and digest.
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.The sorting process is by no means perfect.^ The sorting process is by no means perfect.
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^ Our one of a kind formula and special manufacturing process creates a medicated soap that is perfect for the dispersion of Molluscum No More into skin.

[21]
Periodically, circular muscles at the hindgut's entrance pinch off and excrete a piece of the prostyle, preventing the prostyle from growing too large. .The anus is in the part of the mantle cavity that is swept by the outgoing "lane" of the current created by the gills.^ The anus is in the part of the mantle cavi ty that is swept by the outgoing "lane" of the current created by the gills.
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^ Gastropods (snails) are found in freshwater, and have conquered the land by converting their mantle cavity into a lung (hence their name pulmonate snails) eliminating their primitive gills.

^ If the osphradia detect noxious chemicals or possibly sediment entering the mantle cavity, the gills' cilia may stop beating until the unwelcome intrusions have ceased.
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.Carnivorous molluscs usually have simpler digestive systems.^ Carnivorous molluscs usually have simpler digestive systems.
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[21]

Nervous system

.Molluscs have two pairs of main nerve cords (three in bivalves) the visceral cords serving the internal organs and the pedal ones serving the foot.^ In higher vertebrates, other parts of the skeleton serve as attachment for muscles and for protection of internal organs of the thoracic cavity and the abdomen.
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^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
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^ There is a small brain and two lateral nerve cords joined by cross branches.
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.Both pairs run below the level of the gut, and include ganglia as local control centers in important parts of the body.^ Large branching nerves originating in these ganglia innervate all parts of the body, while several small ganglia are associated with sense organs.
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^ Both segmentation and an ample coelom are important advances, facilitat- ing the development of specialization of parts.
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.Most pairs of corresponding ganglia on both sides of the body are linked by commissures (relatively large bundles of nerves).^ Nervous and Sensory - The greater portion of the gastropod nervous system, called the brain, consists of nine large ganglia, eight of which are paired.
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^ Nervous and Sensory - The muscles are activated by two nerves that run the length of the nematode on both the dorsal and ventral side.
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^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
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.The only ganglia above the gut are the cerebral ganglia, which sit above the esophagus (gullet) and handle "messages" from and to the eyes.^ The only ganglia above the gut are the cerebral ganglia, which sit above the esophagus (gullet) and handle "messages" from and to the eyes.
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^ In Aplysia califonica , the neurons are located in the H-cluster, the only cluster among a total of 13 that is not present bilaterally in the cerebral ganglia.
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^ The pedal ganglia, which control the foot, are just below the esophagus and their commissure and connections to the cerebral ganglia encircle the esophagus in a nerve ring.
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.The pedal ganglia, which control the foot, are just below the esophagus and their commissure and connections to the cerebral ganglia encircle the esophagus in a nerve ring.^ The pedal ganglia, which control the foot, are just below the esophagus and their commissure and connections to the cerebral ganglia encircle the esophagus in a nerve ring.
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^ The perioesophageal nerve-ring of Chaetopoda and Arthropoda is represented, not by the collar first mentioned in the above description, but by the commissures connecting the cerebral and pedal ganglia.

^ The ventral nerve has a series of nerve centers along its length, and both nerves connect to a nerve ring and additional nerve centers located near the head (see Figure 08b).
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[21]
.The brain, in species that have one, encircles the esophagus.^ The brain, in species that have one, encircles the esophagus .
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Most molluscs have a head with eyes, and all have a pair of sensor-containing tentacles, also on the head, that detect chemicals, vibrations and touch.[21]

Reproduction

Apical tuft (cilia)
Prototroch (cilia)
Stomach
Mouth
Metatroch (cilia)
Mesoderm
Anus
/// = cilia
Trochophore larva[29]
.The simplest molluscan reproductive system relies on external fertilization, but there are more complex variations.^ The more complex animals have organ systems to carry out these functions; in simple animals, these functions sometimes are carried out by specialized tissues.
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^ Because this function is carried out by a vascular system in more complex animals, the cavity is known as a gastrovascular cavity.
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^ There is usually no need for external water to accomplish fertilization because the penis of the male passes sperm directly to the female.
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.All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults.^ Immune system reorganization may serve to eliminate unnecessary lymphocytes that could be destructive if they recognized newly emerging adult-specific antigens on the adult tissues.
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.Two gonads sit next to the coelom that surrounds the heart and shed ova or sperm into the coleom, from which the nephridia extract them and emit them into the mantle cavity.^ The nephridia empty into the mantle cavity.
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^ The anus opens into the mantle cavity near the edge of the mantle and the shell (see Figure 11).
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^ The lifecycle of most starfishes starts by shedding their eggs and sperm freely into the water, so fertilization is externally.
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.Molluscs that use such a system remain of one sex all their lives and rely on external fertilization.^ Such a circulatory system is called an open circulatory system because the blood is not contained within blood vessels all the time.
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^ Such systems probably exist in all phyla.
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.Some molluscs use internal fertilization and/or are hermaphrodites, functioning as both sexes; both of these methods require more complex reproductive systems.^ Reproductive - The earthworms are hermaphroditic, with a complete set of organs for both sexes.
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^ Fertilization is the process whereby two sex cells (gametes) fuse together to create a new individual with genetic potentials derived from both parents.
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^ The more complex animals have organ systems to carry out these functions; in simple animals, these functions sometimes are carried out by specialized tissues.
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[21]
.The most basic molluscan larva is a trochophore which is planktonic and feeds on floating food particles by using the two bands of cilia round its "equator" to sweep food into the mouth, which uses more cilia to drive them into the stomach, which uses further cilia to expel undigested remains through the anus.^ Food passes from the frog's mouth into the stomach by way of the esophagus.
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^ Food particles and water enter the mantle cavity by way of the incurrent siphon (Figure 10), a posterior opening between the two valves.
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^ Digestive - The head of a nematode has a few tiny sense organs, and a mouth opening into a muscular pharynx where food (mostly bacteria and detritus) is pulled in and crushed.
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New tissue grows in the bands of mesoderm in the interior, so that the apical tuft and anus are pushed further apart as the animal grows. .The trochophore stage is often succeeded by a veliger stage in which the prototroch, the "equatorial" band of cilia nearest the apical tuft, develops into the velum ("veil"), a pair of cilia-bearing lobes with which the larva swims.^ Fertilization results in a zygote, which develops into a ciliated larva that may swim to a new location.
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^ Some nematodes bear live young, the eggs matured in the female reproductive tract; but most release eggs, which develop into larvae that molt one or more times before reaching maturity.
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^ The shelled egg made development on land possible and eliminated the need for a swimming-larva stage during development.
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.Eventually the larva sinks to the seafloor and metamorphoses into the adult form.^ The zygote develops into a swimming larva that can fend for itself until it develops into the adult form.
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^ Worm-like larvae form a cocoon called a pupa and then become transformed into the adult form.
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.Whilst metamorphosis is the usual state in molluscs, the cephalopods differ in exhibiting direct development: the hatchling is a 'miniaturized' form of the adult.^ The zygote develops into a swimming larva that can fend for itself until it develops into the adult form.
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^ The change in body form as an insect grows to adult is called metamorphosis (Figure 16d).
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^ Species that undergo a complete reorganization of the body tissues exhibit complete metamorphosis, in which case they have 3 stages of development: larval stage, pupal stage , and adult stage , for example, the three stages of caterpillar, cocoon, and .
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[30]

Taxonomy

.Opinions vary about the number of classes of molluscs – for example the table below shows eight living classes,[3] and two extinct ones.^ There are three classes of flatworms: one is free living and two are parasitic.
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^ Figure 19a shows all the animal classes with indicators about added features.
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^ Since insects comprise one of the largest animal groups - both in number of species (about 1 million) and in number of individuals, the grasshopper will be used as the anatomical example (Figure 16e), also see a crayfish anatomy in Figure 16b.
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.However some authors combine the Caudofoveata and solenogasters into one class, the Aplacophora.^ These animals belong to the classes Chilopoda (see Figure 15C) and Diplopoda (it has 2 segments fused into one - 2 pairs of legs for each segment).
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[23][31] Two of the commonly-recognized classes are known only from fossils[2]
Class Major organisms Described living species[3] Distribution
Caudofoveata[31] worm-like organisms 120 seabed 200–3,000 metres (660–9,800 ft)
Aplacophora[31] solenogasters, worm-like organisms 200 seabed 200–3,000 metres (660–9,800 ft)
Polyplacophora[32] chitons 1,000 rocky tidal zone and seabed
Monoplacophora[22] limpet-like organisms 31 seabed 1,800–7,000 metres (5,900–23,000 ft); one species 200 metres (660 ft)
Gastropoda[33] abalone, limpets, conch, nudibranchs, sea hares, sea butterfly, snails, slugs 70,000 marine, freshwater, land
Cephalopoda[34] squid, octopus, cuttlefish, nautilus 900 marine
Bivalvia[35] clams, oysters, scallops, geoducks, mussels 20,000 marine, freshwater
Scaphopoda[19] tusk shells 500 marine 6–7,000 metres (20–22,966 ft)
Rostroconchia[36] fossils; probable ancestors of bivalves extinct marine
Helcionelloida[37] fossils; snail-like organisms such as Latouchella extinct marine

Evolution

Fossil record

There is debate about whether some Ediacaran and Early Cambrian fossils really are molluscs. .Kimberella, from about 555 million years ago, has been described as "mollusc-like",[38][39] but others are unwilling to go further than "probable bilaterian".[40][note 2][41] There is an even sharper debate about whether Wiwaxia, from about 505 million years ago, was a mollusc, and much of this centers on whether its feeding apparatus was a type of radula or more similar to that of some polychaete worms.^ A note on Renea (Caziotia) singularis (Pollonera) and some other members of the Aciculidae (Prosobranchia).-- Basteria, 39 (1-2): 9-13.
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

[40][42] Nicholas Butterfield, who opposes the idea that Wiwaxia was a mollusc, has written that earlier microfossils from 515 to 510 million years ago are fragments of a genuinely mollusc-like radula.[43]
The tiny Helcionellid fossil Yochelcionella is thought to be an early mollusc[37]
Spirally-coiled shells appear in many gastropods[16]
However, the Helcionellids, which first appear over 540 million years ago in Early Cambrian rocks from Siberia and China,[44][45] are thought to be early molluscs with rather snail-like shells. Shelled molluscs therefore predate the earliest trilobites.[37] Although most helcionellid fossils are only a few millimeters long, specimens a few centimeters long have also been found, most with more limpet-like shapes. There have been suggestions that the tiny specimens were juveniles and the larger ones adults.[46]
Some analyses of helcionellids concluded that these were the earliest gastropods.[47] However other scientists are not convinced that Early Cambrian fossils show clear signs of the torsion that identifies modern gastropods twists the internal organs so that the anus lies above the head.[16][48][49]
    = Septa
    = Siphuncle
Septa and siphuncle in nautiloid shell
For a long time it was thought that Volborthella, some fossils of which pre-date 530 million years ago, was a cephalopod. However discoveries of more detailed fossils showed that Volborthella’s shell was not secreted but built from grains of the mineral silicon dioxide (silica), and that it was not divided into a series of compartments by septa as those of fossil shelled cephalopods and the living Nautilus are. .Volborthella’s classification is uncertain.^ Volborthella ’s classification is uncertain.
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^ Volborthella s classification is uncertain.
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[50] The Late Cambrian fossil Plectronoceras is now thought to be the earliest clearly cephalopod fossil, as its shell had septa and a siphuncle, a strand of tissue that Nautilus uses to remove water from compartments that it has vacated as it grows, and which is also visible in fossil ammonite shells. However, Plectronoceras and other early cephalopods crept along the seafloor instead of swimming, as their shells contained a "ballast" of stony deposits on what is thought to be the underside and had stripes and blotches on what is thought to be the upper surface.[51] All cephalopods with external shells except the nautiloids became extinct by the end of the Cretaceous period 65 million years ago.[52] However, the shell-less Coleoidea (squid, octopus, cuttlefish) are abundant today.[53]
The Early Cambrian fossils Fordilla and Pojetaia are regarded as bivalves.[54][55][56][57] "Modern-looking" bivalves appeared in the Ordovician period, 488 to 443 million years ago.[58] One bivalve group, the rudists, became major reef-builders in the Cretaceous, but became extinct in the Cretaceous-Tertiary extinction.[59] However, bivalves are now abundant and diverse.

Phylogeny

A possible "family tree" of molluscs (2007).^ A possible "family tree" of molluscs (2007).
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^ The phylogeny (evolutionary "family tree") of molluscs is a controversial subject.
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[60][61] Does not include annelid worms as the analysis concentrated on fossilizable "hard" features.[60]
The phylogeny (evolutionary "family tree") of molluscs is a controversial subject. In addition to the debates about whether Kimberella and any of the "halwaxiids" were molluscs or closely related to molluscs,[39][40][42][43] there are debates about the relationships between the classes of living molluscs.[41] In fact some groups traditionally classifed as molluscs may have to be redefined as distinct but related.[62]
Molluscs are generally regarded members of the Lophotrochozoa,[60] a group defined by having trochophore larvae and, in the case of living Lophorata, a feeding structure called a lophophore. The other members of the Lophotrochozoa are the annelid worms and seven marine phyla.[63] The diagram on the right summarizes a phylogeny presented in 2007.
Because the relationships between the members of the family tree are uncertain, it difficult to identify the features inherited from the last common ancestor of all molluscs.[64] For example it is uncertain whether the ancestral mollusc was metameric (composed of repeating units) - if it was, that would suggest an origin from an annelid-like worm.[65] Scientists disagree about this: Giribet and colleagues concluded in 2006 that the repetition of gills and of the foot's retractor muscles were later developments, [9] while in 2007 Sigwart concluded that the ancestral mollusc was metameric, and that it had a foot used for creeping and a "shell" that was mineralized.[41] In one particular one branch of the family tree, the shell of conchiferans is thought to have evolved from the spicules (small spines) of aplacophorans; however this is difficult to reconcile with the embryological origins of spicules.[64]
The molluscan shell appears to have originated from a mucus coating, which eventually stiffened into a cuticle. This would have been impermeable and thus forced the development of more sophisticated respiratory apparatus in the form of gills.[37] Eventually, the cuticle would have become mineralized,[37] using the same genetic machinery (engrailed) as most other bilaterian skeletons.[65] The first mollusc shell almost certainly was reinforced with the mineral aragonite.[66]
The evolutionary relationships within the molluscs are also debated, and the diagrams below show two widely-supported reconstructions:
.However, an analysis in 2009 that used both morphological and molecular phylogenetics comparisons concluded that the molluscs are not monophyletic; in particular, that Scaphopoda and Bivalvia are both separate, monophyletic lineages unrelated to the remaining molluscan classes – in other words that the traditional phylum Mollusca is polyphyletic, and that it can only be made monophyletic if scaphopods and bivalves are excluded.^ Only permits of Class A, B, C, and D will be made available for initial issuance.
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[62] A 2010 analysis similarly concluded that the molluscs are not monophyletic, this time suggesting that solenogastres are more closely related to the non-molluscan taxa used as an outgroup than to other molluscs.[67]

Relations with humans

Uses by humans

Mollusc output in 2005
Molluscs, especially bivalves such as clams and mussels, have been an important food source since at least the advent of anatomically modern humans – and this has often resulted in over-fishing.[68] Other commonly eaten molluscs include octopuses and squids, whelks, oysters, and scallops.[69] In 2005, China accounted for 80% of the global mollusc catch, netting almost 11,000,000 tonnes (11,000,000 LT; 12,000,000 ST). .Within Europe, France remained the industry leader.^ Within Europe, France remained the industry leader.
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[70] Some countries regulate importation and handling of molluscs and other seafood, mainly to minimize the poison risk from toxins that accumulate in the animals.[71]
Photo of three circular metal cages in shallows, with docks, boathouses and palm trees in background
Saltwater pearl oyster farm in Seram, Indonesia
Most molluscs that have shells can produce pearls, but only the pearls of bivalves and some gastropods whose shells are lined with nacre are valuable.[16][18] The best natural pearls are produced by pearl oyster.s Pinctada margaritifera and Pinctada mertensi, which live in the tropical and sub-tropical waters of the Pacific Ocean. Natural pearls form when a small foreign object gets stuck between the mantle and shell.
.There are two methods of culturing pearls, by inserting either "seeds" or beads into oysters.^ There are two methods of culturing pearls, by inserting either "seeds" or beads into oysters.
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^ The layering of calcium carbonate crystals that is characteristic of natural pearls, tissue-cultured pearls, bead-cultured pearls and the nacre layer of bead-and-tissue-cultured pearls.
  • My String Of Pearls - Pearl Terms, Definitions & Glossary 21 January 2010 18:018 UTC mystringofpearls.com [Source type: Reference]

^ In saltwater bivalve pearl-producing mollusks, the reproductive organ where a bead nucleus or nuclei and donor-mollusk tissue piece or pieces are implanted to produce cultured pearls.
  • My String Of Pearls - Pearl Terms, Definitions & Glossary 21 January 2010 18:018 UTC mystringofpearls.com [Source type: Reference]

The "seed" method uses grains of ground shell from freshwater mussels, and over-harvesting for this purpose has endangered several freshwater mussel species in the southeastern USA.[18] The pearl industry is so important in some areas that significant sums of money are spent on monitoring the health of farmed molluscs.[72]
Other luxury and high-status products were made from molluscs. Tyrian purple, made from the ink glands of murex shells, "... fetched its weight in silver" in the fourth-century BC, according to Theopompus.[73] The discovery of large numbers of Murex shells on Crete suggests that the Minoans may have pioneered the extraction of "Imperial purple" during the Middle Minoan period in the 20th–18th century BC, centuries before the Tyrians.[74][75] Sea silk is a fine, rare and valuable fabric produced from the long silky threads (byssus) secreted by several bivalve molluscs, particularly Pinna nobilis, to attach themselves to the sea bed.[76] Procopius, writing on the Persian wars circa 550 CE, "stated that the five hereditary satraps (governors) of Armenia who received their insignia from the Roman Emperor were given chlamys (or cloaks) made from lana pinna (Pinna "wool," or byssus). .Apparently only the ruling classes were allowed to wear these chlamys."^ Apparently only the ruling classes were allowed to wear these chlamys."
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[77]
Mollusc shells, including those of cowries, were used as a kind of money in several pre-industrial societies. .However these "currencies" generally differed in important ways from the standardized government-backed and -controlled money familiar to industrial societies.^ However these "currencies" generally differed in important ways from the standardized government-backed and -controlled money familiar to industrial societies.
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^ The pearl industry is so important in some areas that significant sums of money are spent on monitoring the health of farmed molluscs.
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^ Mollusc shells, including those of cowries , were used as a kind of money in several pre-industrial societies.
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Some shell "currencies" were not used for commercial transactions but mainly as social status displays at important occasions such as weddings.[78] When used for commercial transactions they functioned as commodity money, in other words as a tradable commodity whose value differed from place to place, often as a result of difficulties in transport, and which was vulnerable to incurable inflation if more efficient transport or "goldrush" behavior appeared.[79]

Threats to humans

Stings and bites

The blue-ringed octopus's rings are a warning signal – this octopus is alarmed, and its bite can kill.[80]
When handled alive, a few species of molluscs can sting or bite, and for some species, this can present a serious risk to the human who is handling the animal. .To put this into the correct perspective however, deaths from mollusc venoms are less than 10% of the number of deaths from jellyfish stings.^ No more than 10 percent of the maximum number of permits, of all size classes combined, may be held by the same permit holder.
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[81]
All octopuses are venomous[82] but only a few species pose a significant threat to humans. .Blue-ringed octopuses in the genus Hapalochlaena, which live around Australia and New Guinea, bite humans only if severely provoked,[80] but their venom kills 25% of human victims.^ Thiara cybele (Gould, 1847) Papua New Guinea: Milne Bay: : 0.25 mi.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

^ Melanoides aspirans (Hinds) Papua New Guinea: Milne Bay: : 0.25 to 0.5 mi.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

^ Melanoides Olivier, 1804 Papua New Guinea: Milne Bay: : Varer Village (Juro), Tagula Island, 0.25 mi.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

Another tropical species, Octopus apollyon, causes severe inflammation that can last for over a month even if treated correctly.[83]
Photo of cone on ocean bottom
Live cone snails can be dangerous to shell-collectors but are useful to neurology researchers[84]
.Cone snails, carnivorous gastropods that feed on marine invertebrates (and in the case of larger species on fish), produce a huge array of toxins, some fast-acting and others slower but deadlier – they can afford to do this because their toxins require less time and energy to be produced compared with those of snakes or spiders.^ Trigger fishes (Those species not Balistidae.
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^ Detailed billing with receipts and supporting records are required for allowable communication and lost fishing time claims.
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^ Fish within any protected species study zone in the NWHI without notifying the Regional Administrator of the intent to fish in these zones, as required under Sec.
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[84] .Many painful stings have been reported and a few fatalities, although some of the reported fatalities may be exaggerations.^ Many painful stings have been reported and a few fatalities, although some of the reported fatalities may be exaggerations.
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[81] .Only the few larger species of cone snail that can capture and kill fish are likely to be seriously dangerous to humans.^ NMFS will reimburse the owner only for those days during which the vessel is unable to fish as a direct result of helping the NMFS employee who is seriously injured or seriously ill.
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[85] .The effects of individual cone shell toxins on victims' nervous systems are so precise that they are useful tools for research in neurology, and the small size of their molecules makes it easy to synthesize them.^ The effects of individual cone shell toxins on victims' nervous systems are so precise that they are useful tools for research in neurology , and the small size of their molecules makes it easy to synthesize them.
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^ Live cone snails can be dangerous to shell-collectors but are useful to neurology researchers [76 ] Cone snails , carnivorous gastropods which feed on marine invertebrates (and in the case of larger species on fish), produce a huge array of toxins , some fast-acting and others slower but deadlier they can afford to do this because their toxins are relatively "cheap" to make compared with those of snakes or spiders.
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^ Both systems use chemical signals to bring about a desired response in some target, perhaps a muscle (in the case of the nervous system) or the liver (in the case of the endocrine system).
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[84][86]
The traditional belief that a giant clam can trap the leg of a person between its valves, thus drowning them, is a myth.[87]

Pests

Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is "second only to malaria as the most devastating parasitic disease in tropical countries. .An estimated 200 million people in 74 countries are infected with the disease — 100 million in Africa alone."^ An estimated 200 million people in 74 countries are infected with the disease 100 million in Africa alone."
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^ Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is transmitted to humans via water snail hosts, and affects about 200 million people.
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^ Estimated 7 million specimens arranged in more than 200,000 lots.
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  • INHS Mollusk Collection | Systematic Research Collections 21 January 2010 18:018 UTC www.inhs.uiuc.edu [Source type: Academic]

[88] .The parasite has 13 known species, of which two infect humans.^ The parasite has 13 known species, of which two infect humans.
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The parasite itself is not a mollusc, but all the species have freshwater snails as intermediate hosts.[89]
Some species of molluscs, particularly certain snails and slugs, can be serious crop pests,[90] and snails or slugs introduced into new environments can unbalance local ecosystems. .One such pest, the giant African snail Achatina fulica, has been introduced to many parts of Asia, as well as to many islands in the Indian Ocean and Pacific Ocean.^ Pacific remote island areas (PRIA, or U.S. island possessions in the Pacific Ocean) means Palmyra Atoll, Kingman Reef, Jarvis Island, Baker Island, Howland Island, Johnston Atoll, Wake Island, and Midway Atoll.
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In the 1990s this species reached the West Indies. Attempts to control it by introducing the predatory snail Euglandina rosea proved disastrous, as the predator ignored Achatina fulica and went on to extirpate several native snail species instead.[91]
Despite its name, Molluscum contagiosum is a viral disease, and is unrelated to molluscs.[92]

Notes

  1. ^ Spelled mollusk in the USA, see reasons given in Rosenberg's [1]; for the spelling "mollusc" see the reasons given by Brusca & Brusca. Invertebrates (2nd ed.). .
  2. ^ It is possible that Kimberella is more closely related to, for instance, the brachiopods than the molluscs

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  61. ^ "The Mollusca". University of California Museum of Paleontology. http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php. Retrieved 2008-10-02. 
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  63. ^ "Introduction to the Lophotrochozoa". University of California Museum of Paleontology. http://www.ucmp.berkeley.edu/phyla/lophotrochozoa.html. Retrieved 2008-10-02. 
  64. ^ a b Henry, J.; Okusu, A.; Martindale, M. (2004). "The cell lineage of the polyplacophoran, Chaetopleura apiculata: variation in the spiralian program and implications for molluscan evolution". Developmental biology 272 (1): 145–160. doi:10.1016/j.ydbio.2004.04.027. PMID 15242797.  edit
  65. ^ a b Jacobs, D. K. (2000). "Molluscan engrailed expression, serial organization, and shell evolution". Evolution & Development 2: 340–347. doi:10.1046/j.1525-142x.2000.00077.x.  edit
  66. ^ Porter, S. M. (Jun 2007). "Seawater chemistry and early carbonate biomineralization". Science (New York, N.Y.) 316 (5829): 1302–1301. doi:10.1126/science.1137284. ISSN 0036-8075. PMID 17540895.  edit
  67. ^ Wilson, N.; Rouse, G.; Giribet, G. (2010). "Assessing the molluscan hypothesis Serialia (Monoplacophora+Polyplacophora) using novel molecular data.". Molecular phylogenetics and evolution 54 (1): 187–193. doi:10.1016/j.ympev.2009.07.028. PMID 19647088.  edit
  68. ^ Mannino, M.A., and Thomas, K.D. (February 2002). "Depletion of a resource? The impact of prehistoric human foraging on intertidal mollusc communities and its significance for human settlement, mobility and dispersal". World Archaeology 33 (3): 452–474. doi:10.1080/00438240120107477. 
  69. ^ Garrow, J.S., Ralph, A., and James, W.P.T. (2000). Human Nutrition and Dietetics. Elsevier Health Sciences. pp. 370. ISBN 0443056277. 
  70. ^ "China catches almost 11 m tonnes of molluscs in 2005". FAO. http://www.fao.org/figis/servlet/TabLandArea?tb_ds=Capture&tb_mode=TABLE&tb_act=SELECT&tb_grp=COUNTRY. Retrieved 2008-10-03. 
  71. ^ "Importing fishery products or bivalve molluscs". United Kingdom: Food Standards Agency. http://www.food.gov.uk/foodindustry/imports/want_to_import/fisheryproducts/. Retrieved 2008-10-02. 
  72. ^ Jones, J.B., and Creeper, J. (April 2006). "Diseases of Pearl Oysters and Other Molluscs: a Western Australian Perspective". Journal of Shellfish Research 25 (1): 233–238. doi:10.2983/0730-8000(2006)25[233:DOPOAO2.0.CO;2]. 
  73. ^ The fourth-century BC historian Theopompus, cited by Athenaeus (12:526) around 200 BC ; according to Gulick, C.B. (1941). Athenaeus, The Deipnosophists. Cambridge, Mass.: Harvard University Press. 
  74. ^ Reese, D.S. (1987). "Palaikastro Shells and Bronze Age Purple-Dye Production in the Mediterranean Basin". Annual of the British School of Archaeology at Athens 82: 201–6. 
  75. ^ Stieglitz, R.R. (1994). "The Minoan Origin of Tyrian Purple". Biblical Archaeologist 57: 46–54. doi:10.2307/3210395. 
  76. ^ Webster's Third New International Dictionary (Unabridged) 1976. G. & C. Merriam Co., p. 307.
  77. ^ Turner, R.D., and Rosewater, J. (June 1958). "The Family Pinnidae in the Western Atlantic". Johnsonia 3 (38): 294. 
  78. ^ Maurer, B. (October 2006). "The Anthropology of Money". Annual Review of Anthropology 35: 15–36. doi:10.1146/annurev.anthro.35.081705.123127. http://www.anthro.uci.edu/faculty_bios/maurer/Maurer-AR.pdf. Retrieved 2008-10-23. 
  79. ^ Hogendorn, J., and Johnson, M. (2003). The Shell Money of the Slave Trade. Cambridge University Press. ISBN 052154110.  Particularly chapters "Boom and slump for the cowrie trade" (pages 64-79) and "The cowrie as money: transport costs, values and inflation" (pages 125-147)
  80. ^ a b Alafaci, A.. "Blue ringed octopus". Australian Venom Research Unit. http://www.avru.org/compendium/biogs/A000060b.htm. Retrieved 2008-10-03. 
  81. ^ a b Williamson, J.A., Fenner, P.J., Burnett, J.W., and Rifkin, J. (1996). Venomous and Poisonous Marine Animals: A Medical and Biological Handbook. UNSW Press. pp. 65–68. ISBN 0868402796. http://books.google.co.uk/books?id=YsZ3GryFIzEC&pg=PA75&lpg=PA75&dq=mollusc+venom+fatal&source=web&ots=tBDHW2xdlx&sig=PAvTz2z3hnwUyE4lfU8fvzwNbD4&hl=en&sa=X&oi=book_result&resnum=2&ct=result#PPA57,M1. Retrieved 2008-10-03. 
  82. ^ Anderson, R.C. (1995) Aquarium husbandry of the giant Pacific octopus. Drum and Croaker 26:14-23
  83. ^ Brazzelli, V., Baldini, F., Nolli, G., Borghini, F., and Borroni, G. (1999). "Octopus apollyon bite". Contact Dermatitis 40 (3): 169–170. doi:10.1111/j.1600-0536.1999.tb06025.x. 
  84. ^ a b c Concar, D. (19 October 1996). "Doctor snail – Lethal to fish and sometimes even humans, cone snail venom contains a pharmacopoeia of precision drugs". New Scientist. http://environment.newscientist.com/article/mg15220523.900-doctor-snail--lethal-to-fish-and-sometimes-even-humans-cone-snail-venom-contains-apharmacopoeia-of-precision-drugs-itdavid-concarit-finds-out-how-the-toxinstarget-nerve-cells.html. Retrieved 2008-10-03. 
  85. ^ Livett, B.. "Cone Shell Mollusc Poisoning, with Report of a Fatal Case". Department of Biochemistry and Molecular Biology, University of Melbourne. http://grimwade.biochem.unimelb.edu.au/cone/deathby.html. 
  86. ^ Haddad, V.(junior), de Paula Neto, J.B., and Cobo, V.J. (September-October 2006). Venomous mollusks: the risks of human accidents by Conus snails (Gastropoda: Conidae) in Brazil. 39. pp. 498–500. http://www.scielo.br/pdf/rsbmt/v39n5/a15v39n5.pdf. Retrieved 2008-10-03. 
  87. ^ Cerullo, M.M., Rotman, J.L., and Wertz, M. (2003). The Truth about Dangerous Sea Creatures. Chronicle Books. pp. 10. ISBN 0811840506. http://books.google.co.uk/books?hl=en&lr=&id=1MOxNDmFLd4C&oi=fnd&pg=PA1&dq=giant+clam+trap+foot&ots=lYe_I4NhIO&sig=0KwRdmEoB4rt6zk1lvxPdiH_jkE#PPA10,M1. Retrieved 2008-10-03. 
  88. ^ "The Carter Center Schistosomiasis Control Program". The Carter Center. http://www.cartercenter.org/health/schistosomiasis/index.html. Retrieved 2008-10-03. 
  89. ^ Brown, D.S. (1994). Freshwater Snails of Africa and Their Medical Importance. CRC Press. pp. 305. ISBN 0748400265. 
  90. ^ Barker, G.M. (2002). Molluscs As Crop Pests. CABI Publications. ISBN 0851993206. 
  91. ^ Civeyrel, L., and Simberloff, D. (October 1996). "A tale of two snails: is the cure worse than the disease?". Biodiversity and Conservation 5 (10): 1231–1252. doi:10.1007/BF00051574. 
  92. ^ "Molluscum (Molluscum Contagiosum): Frequently Asked Questions for Everyone". Centers for Disease Control and Prevention. http://www.cdc.gov/ncidod/dvrd/molluscum/faq/everyone.htm. Retrieved 2008-10-03. 

Further reading

  • Starr & Taggart (2002). Biology: The Unity and Diversity of Life. Pacific Grove, California: Thomson Learning. 
  • Nunn, J.D., Smith, S.M., Picton, B.E. and McGrath, D. 2002. Checklist, atlas of distribution and bibliography for the marine mollusca of Ireland. in. Marine Biodiversity in Ireland and Adjacent Waters. Ulster Museum. publication no. 8.

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

.MOLLUSCA, one of the great " phyla," or sub-kingdoms, of the animal pedigree or kingdom.^ A.  Most known organisms are animals (kingdom Animalia)      1.  Of the 1.5 million known species, one-third are animals.

The shell-bearing forms belonging to this group which were known to Linnaeus were placed by him (in 1748) in the third order of his class Vermes under the name " Testacea," whilst the Echinoderms, Hydroids and Annelids, with the naked Mollusca, formed his second order termed " Zoophyta." Ten years later he replaced the name " Zoophyta " by " Mollusca," which was thus in the first instance applied, not to the Mollusca at present so termed, but to a group consisting chiefly of other organisms. .Gradually, however, the term Mollusca became used to include those Mollusca formerly placed among the " Testacea," as well as the naked Mollusca.^ The term "conchology" is also used for the study of molluscs; however, it is usually applied to those that study the shell only.

^ During the turn of the century the collections became part of the University of Amsterdam and now includes the well known Schepman collection.
  • Systematic Research Collections: Mollusca 21 January 2010 18:018 UTC www.inhs.illinois.edu [Source type: Academic]

.It is important to observe that the term µaXaiaa, of which Mollusca is merely a latinized form, was used by Aristotle to indicate a group consisting of the cuttle-fishes only.^ Pharangeal pouches or gill clefts (slits), which are seen only during embryological development in most vertebrate groups, although they persist in adult fishes.
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^ Studies of capsule wall microstructure indicate that whelk capsules consist of a number of discrete layers that are resolvable using light microscopy.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

As now classified, the Mollusca consist of the following subdivisions: - Grade A. - Isopleura.
Class I. - Amphineura (see Chiton).
Grade B. - Prorhipidoglossomorpha.
Class II. - Gastropoda.
Class III. - Scaphopoda.
Class IV. - Lamellibranchia.
Grade C. - Siphonopoda.
Class V. - Cephalopoda.
Table of contents

History of Classification

.The definite erection of the Mollusca into the position of one of the great primary groups of the animal kingdom is due to George Cuvier (1788-1800), who largely occupied himself with the dissection of representatives of this type.^ Changes within a population (a group of organisms of one species) generally occur due to divergence and speciation.

^ Throughout the animal kingdom an incredible variety of embryonic types exists, but most patterns of embryogenesis comprise variations on four themes as shown by the development of a representative organism, the frog, in Figure 19f: .
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ They are represented today by several types of animals, including the lemurs.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

l * .An independent anatomical investigation of the Mollusca had been carried on by the remarkable Neapolitan naturalist Poli (1791), whose researches 2 were not published until after his death (1817), and were followed by the beautiful works of another Neapolitan zoologist, the illustrious Delle Chiaje.3 The embranchement or sub-kingdom Mollusca, as defined by Cuvier, included the following classes of shellfish: (1) the cuttles or poulps, under the name Cephalopoda; (2) the snails, whelks and slugs, both terrestrial and marine, under the name Gastropoda; (3) the sea-butterflies or winged-snails, under the name Pteropoda; (4) the clams, mussels and oysters, under the name Acephala; (5) the lamp-shells, under the name Brachiopoda; (6) the seasquirts or ascidians, under the name Nuda; and (7) the barnacles and sea-acorns, under the name Cirrhopoda.^ A. Nudibranchs ("sea slugs") are molluscs closely related to marine snails.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ A. All shells of animals in the phylum mollusca (snails, oysters, clams, etc.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The classification for all other species of octopods is the same up until the genus and species: Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Order: Octopoda Family: Octopodidae Genus: Octopus Species: dofleini .
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The main limitations of the sub-kingdom or phylum Mollusca, as laid down by Cuvier, and the chief divisions thus recognized within its limits by him, hold good to the present day.^ A: Squids are classified in the Kingdom Animalia, Phylum Mollusca, Class Cephalopoda, Subclass Coleoidea, and Order Teuthoidea.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.At the same time, three of the classes considered by him as Mollusca have been one by one removed from that association in consequence of improved knowledge, and one additional class, incorporated since his day with the Mollusca with general approval, has, after more than forty years, been again detached and assigned an independent position owing to newly acquired knowledge.^ About 50% more individuals than in the control culture died within seven days in the presence of NikkomycinZ. As shown in Fig.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ There are three classes of flatworms: one is free living and two are parasitic.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ About three times more individuals than in the control culture were malformed on the 8 th day.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

The first of Cuvier's classes to be removed from the Mollusca was that of the Cirrhopoda. Their affinities with the lower Crustacea were recognized by Cuvier and his contemporaries, but it was one of the brilliant discoveries of that remarkable and too-little-honoured naturalist, J. Vaughan Thompson, of Cork, which decided their position as Crustacea. The metamorphoses of the Cirrhopoda were described and figured by him in 1830 in a very complete manner, and the legitimate conclusion as to their affinities was formulated by him. .4 Thus it is to Thompson (1830), and not to Burmeister (1834), as erroneously stated by Keferstein, that the merit of this discovery belongs.^ Viviparus georgianus (I. Lea, 1834) United States: Illinois: : Thompson Lake (0) ; Collector: unknown; ; Preparation/Count: Dry 6.0 .
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

^ Viviparus georgianus (I. Lea, 1834) United States: Illinois: Fulton: Thompsons Lake USGS 40.3528?N, 90.0765?W (2) ; Collector: orig.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

.The next class to be removed from Cuvier's * These figures refer to the Bibliography at the end of the article.^ These animals belong to the classes Chilopoda (see Figure 15C) and Diplopoda (it has 2 segments fused into one - 2 pairs of legs for each segment).
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Mollusca was that of the Nuda, better known as Tunicata. .In 1866 the Russian embryologist Kowalewsky startled the zoological world with a minute account of the developmental changes of Ascidia, one of the Tunicata, 5 and it became evident that the affinities of that class were with the Vertebrata, whilst their structural agreements with Mollusca were only superficial.^ It is self-evident that NikkomycinZ can be applied for structural studies on mollusc shell formation in vivo in only sublethal concentrations.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

.The last class which has been removed from the Cuvierian Mollusca is that of the Lamp-shells or Brachiopoda.^ The animal that makes it is a kind of snail (Phylum Mollusca: Class Gastropoda), and the shell is part of its body.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

The history of its dissociation is connected with that of the class, viz. the Polyzoa or Bryozoa, which has been both added to and again removed from the Mollusca between Cuvier's date and the present day. The name of J. Vaughan Thompson is again that which is primarily connected with the history of a Molluscan class. .In 1830 he pointed out that among the numerous kinds of " polyps " at that time associated by naturalists with the Hydroids, there were many which had a peculiar and more elaborate type of organization, and for these he proposed the name Polyzoa.^ As demonstrated in C. elegans , many of these genes have apparently functional alleles in one or more wild isolates and therefore are not pseudogenes.
  • BioMed Central | Full text | Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ There is much research underway regarding these tiny snails - there may be many more species than is commonly supposed, and researchers are using modern DNA technologies to try to determine how many different species there are.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ A: Common names for animals usually tend to be a bit ambiguous, since there are many different species of clams which could be known as the soft clam.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

Subsequently 6 they were termed Bryozoa by Ehrenberg (1831).
.Henri Milne-Edwards in 1844 demonstrated the affinities of the Polyzoa with the Molluscan class Brachiopoda, and proposed to associate the three classes Brachiopoda, Polyzoa and Tunicata in a large group " Molluscoidea," co-ordinate with the remaining classes of Cuvier's Mollusca, which formed a group retaining the name Mollusca.^ Comment on the proposed conservation of the specific name of Xerophila geyeri Soós, 1926 (Mollusca, Gastropo- da).
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

^ Xerophila geyeri Soós, 1926 (currently Trochoidea geyeri; Mollusca, Pulmonata): proposed conservation of the specific name.-- Bull.
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

^ Mr48: Marshall, B.A. 2002: Some Recent scissurellids from the New Zealand region and remarks on some scissurellid genus group names (Mollusca : Gastropoda : Vetigastropoda).

.By subsequent writers the Polyzoa have in some cases been kept apart from the Mollusca and classed with the " Vermes "; whilst by others they have, together with the Brachiopoda, been regarded.as true Mollusca.^ We thought they were some garbage some one dropped, but a friend told us they were egg cases for some kind of creature.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Some species have inhalent and exhalent siphons the same length while in others they are quite different.

^ Aplacophorans have a radula and a posterior mantle cavity.  Some are detritus feeders, others are predators.  They range in length from 1 to 300 millimeters.

Increase of knowledge has now, however, established the conclusion that the agreement of structure supposed to obtain between Polyzoa and true Mollusca is delusive; and accordingly they, together with the Brachiopoda, were removed from the Molluscan phylum by Lankester in his article in the 9th edition of this work (on the which present article is based). Further details in regard to this, the last revolution in Molluscan classification, will be found in the article Polyzoa.
.As thus purified by successive advances of embryological research, the Mollusca were reduced to the Cuvierian classes of Cephalopoda, Pteropoda, Gastropoda and Acephala.^ The animal that makes it is a kind of snail (Phylum Mollusca: Class Gastropoda), and the shell is part of its body.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ A: Squids are classified in the Kingdom Animalia, Phylum Mollusca, Class Cephalopoda, Subclass Coleoidea, and Order Teuthoidea.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Phylum Mollusca, Class Cephalopoda, Order Teuthoidea, Family Architeuthidae.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

Certain modifications in the disposition of these classes are naturally enough rendered necessary by the vast accumulation of knowledge as to the anatomy and embryology of the forms comprised in them. .Foremost among those who between 1840 and 1880 laboured in this field are the French zoologists Henri Milne-Edwards° and Lacaze Duthiers, 10 to the latter of whom we owe the most accurate dissections and beautiful illustrations of a number of different types.^ We know very little about the life histories of most of these different types of squid.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

To Kolliker,ll Gegenbaur, 12 and more recently Spenger, l3 amongst German anatomists, we are indebted for epoch-making researches of the same kind. .In England, Owen's anatomy of the pearly nautilus,14 Huxley's discussion of the general morphology of the Mollusca,17 and Lankester's embryological investigations, 19 have aided in advancing our knowledge of the group.^ The cephalopods are an ancient and very successful group, some of which are now the most advanced of all the invertebrates.  They have long been among the dominant large predators in our oceans.

.Two remarkable works of a systematic character dealing with the Mollusca deserve mention here - the Manual of the Mollusca, by Dr S. P. Woodward, a model of clear systematic exposition, and the exhaustive treatise on the Malacozoa or Weichthiere by Professor Keferstein of Gottingen, published as part of Bronn's Klassen and Ordnungen des Thier-Reichs. The arrangement adopted by Ray Lankester in the 9th edition of the Ency.^ Ll1: Leal, J.H. 2008: A remarkable new genus of carnivorous, sessile bivalves (Mollusca: Anomalodesmata: Poromyidae) with descriptions of two new species.

^ Part 1: Systematic descriptions and comparisons based on shell and radular characters.

^ Cm1: Coomans, H.E.; Filmer, R.M. 1985: Studies of Conidae (Mollusca, Gastropoda) 3: Systematics and distribution of some Australian species, including two new taxa.

Brit.
(art. ." Mollusca "; 1883) was as follows: Of the four Cuvierian classes mentioned above, the Pteropoda were united with the Cephalopoda, on account of the apparent similarity of the cephalic tentacles in some of the former to the arms of the latter.^ On Trochoidea geyeri (Soós, 1926) and some conchologically similar taxa (Mollusca: Gastropoda Pulmonata: Hygromiidae).-- Zool.
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

^ Structure of the cephalic tentacles of some species of proso-branch limpet (Patellidae and Fissurellidae).

An additional class was instituted for the reception of Dentalium and its few allies, and for this class Bronn's name Scaphopoda was used. The Chitons and their allies were placed under the Gastropoda, as a distinct branch called Isopleura, and for the Acephala de Blainville's name Lamellibranchia was substituted. .The latter were regarded as forming a distinct branch, equivalent in rank to the other three classes together, the latter all possessing the radula which is wanting in Lamellibranchs.^ Members of all classes except the bivalves possess a ribbon-like set of hooked teeth called radula .

^ Some coil left to right while others loose their coil all together.

^ The tunicates and lancelets sometimes are called the protochordates (Figure 19b) because they possess all three typical chordate structures in either the larval and/or adult forms, as did the first chordates to evolve.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

Since the 9th edition of the Ency. .Brit. was published important advances have been made in our knowledge of the Mollusca, as the result of researches largely due to the interest excited in the subject by Lankester's article.^ The cephalopods are an ancient and very successful group, some of which are now the most advanced of all the invertebrates.  They have long been among the dominant large predators in our oceans.

^ E. (Edi) Mollusca Marine Zoology Permanent Researcher Advanced search .
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

.Attention has been especially directed to the investigation of the most primitive forms in each group, and accordingly we can now form much more definite conceptions of the phylogeny and evolution of the various classes.^ Early evolution and the primitive groups.

^ In the more primitive Protobranchia the foot has a flattened sole on its foot.  The edges of this sole fold together to form a sharp edge.

^ The cephalopods are an ancient and very successful group, some of which are now the most advanced of all the invertebrates.  They have long been among the dominant large predators in our oceans.

.The most important and extensive contributions to this progress have been made by the Belgian zoologist, Dr Paul Pelseneer, who has made the Mollusca his special study.^ An Ecological Study of Two Sympatric Species of Fasciolaria (Mollusca: Gastropoda) in Alligator Harbor, Florida.

.The Chitonidae and the Aplacophora are now separated from the Gastropoda and raised to the rank of a distinct class, under the name of Amphineura.^ Validation under the plenary powers of specific names for nine species of the class Gastropoda occurring in the New Zealand area as published by Martyn (T.) in 1784 in the work entitled The Universal Conchologist (Opinion supplementary to Opinion 456).

.On the other hand, Boas and Pelseneer have shown that the Pteropoda have nothing to do with the Cephalopoda, but are Gastropoda modified for a pelagic life; they are therefore now united with the Gastropoda.^ Molluscan sperm ultrastructure: correlation with taxonomic units within the Gastropoda, Cephalopoda and Bivalvia.

^ The life of an octopus is short, even at the Vancouver Aquarium, when their female octopus lays her eggs they know she is at the end of her life and there is nothing much they can do.
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^ They are all marine inhabitants, and many have adapted to a pelagic or swimming style of life.  Most are herbivorous, but many are parasitic (e.g.

.The Lamellibranchia are no longer regarded as a distinct branch in contrast to the remaining Mollusca; according to Pelseneer they are allied to the Gastropoda and Scaphopoda, all three classes being derived from a common hypothetical ancestor, called Prorhipidoglossum. These three classes have therefore been united by Grobben into one branch or grade, the Prorhipidoglossomorpha.^ These are another group in the phylum Mollusca, called the class Bivalvia.
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^ As demonstrated in C. elegans , many of these genes have apparently functional alleles in one or more wild isolates and therefore are not pseudogenes.
  • BioMed Central | Full text | Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ There are three classes of flatworms: one is free living and two are parasitic.
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General Characters of the Mollusca

.The forms comprised in the various groups, whilst exhibiting an extreme range of variety in shape, as may be seen on comparing an oyster, a cuttle-fish, and a sea-slug such as Doris; whilst adapted, some to life on dry land, others to the depths of the sea, others to rushing streams; whilst capable, some of swimming, others of burrowing, crawling or jumping, some, on the other hand, fixed and immobile; some amongst the most formidable of carnivores, others feeding on vegetable mud, or on the minutest of microscopic organisms - yet all agree in possessing in common a very considerable number of structural details which are not possessed in common by any other animals.^ The cephalopods are adapted for a carnivorous diet, and eat a variety of crustaceans, molluscs, fish and other marine animals.
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^ Respiratory - Snails are adapted to life on land.
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^ Like other animals, whelks exhibit a variety of developmental patterns.
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.The structural features which the Mollusca do possess in common with other animals belonging to other great phyla of the animal kingdom are those characteristic of the Coelomata, one of the two great grades (the other and lower being that of the Coelentera) into which the higher animals; or Metazoa as distinguished from the Protozoa, are divided.^ Propodial elaboration in southern African and Indian Ocean Fissurellidae (Mollusca: Prosobranchia) with descriptions of two new genera and one new species.

^ Among the chordates are those animals with which we are most familiar, including human beings.
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^ There are also two types of circular muscles, one type contracts for slow swimming and the other contract for fast escape swimming.
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.The Metazoa all commence their individual existence as a single cell or plastid, which multiplies itself by transverse division.^ Thus, it is often said that sex is deadly, and despite all the human aspiration to higher level of existence, we are basically the carrier of germ cells.
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^ Digestion is always at least partially extracellular in gastropods - there are no gastropod species where all digestion takes place inside the individual cells.

.Unlike the cells of Protozoa, these embryonic cells of the Metazoa do not remain each like its neighbour and capable of independent life, but proceed to arrange themselves into two layers, taking the form of a sac.^ Two layers of cells .
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^ At one time, both body forms may have been a part of the life cycle of all cnidarians, because today we see an alternation of generations life cycle of these two forms in certain cnidarians (see Figure 05d).
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^ The calcium carbonate layers are generally of two types: an outer, chalk-like prismatic layer and an inner pearly lamellar or nacreous layer.
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.The cavity of the two-cell-layered sac or diblastula thus formed is the primitive gut or arch-enteron.^ Two layers of cells .
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^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ In echinoderms and chordates, the coelom forms by outpocketing of the primitive gut.
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.In the Coelentera, whatever subsequent changes of shape the little sac may undergo as it grows up to be polyp or jelly-fish, the original arch-enteron remains as the one cavity pervading all regions of the body.^ The clams extend their muscular siphons (they may have one or two) up to the surface of the sand and use it like a straw to suck in large quantities of water.
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^ All information specified by the Regional Administrator must be recorded on paper or electronically within 24 hours after the completion of each fishing day.
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^ At one time, both body forms may have been a part of the life cycle of all cnidarians, because today we see an alternation of generations life cycle of these two forms in certain cnidarians (see Figure 05d).
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.In the Coelomata, on the other hand, there is another cavity, dividing the body-wall into two layers: an internal layer surrounding the gut, and an external layer.^ Typically, echinoderms have an endoskeleton (internal skeleton) consisting of hard calcite ossicles embedded in the body wall and often bearing protruding spines or tubercles.
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^ Food entering the mouth is passed anteriorly to the stomach via ciliary action.  The stomach is surrounded by a large digestive gland and is divided into two regions.  In the first region ( dorsal ) the esophagus and ducts of the digestive gland enter and it contains a ventral style sac.

^ The mesohyl is a gelatinous layer between the outer body of the sponge and the spongocoel (the inner cavity).
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.This cavity is excavated in a third mass of cells distinct from the cells lining the gut, forming the endoderm, and the cells covering the surface of the body, the ectoderm.^ In vertebrates, the mid-dorsal ectodermal cells fold to form the neural tube with the notochord laying under.
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^ For example, they would pick up some food, move out to the sheets of cells that cover the surface, and feed them.
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^ In the early embryonic stages of mollusc development, differentiated ectodermal cells form the shell field, a tissue that excretes the larval shell, as reviewed by Kniprath [ 41 ].
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

This third mass of cells is the mesoderm. The Mollusca agree in being coelomate with the phyla Vertebrata, Platyhelmia (flat-worms), Echinoderma, Appendiculata (insects, ringed-worms, &c.), and others - in fact, with all the Metazoa except the sponges, corals, polyps, and medusae.
.In common with all other Coelomata, the Mollusca are at one period of life possessed of a prostomium or region in front of the mouth, which is the essential portion of the " head," and is connected with the property of forward locomotion in a definite direction and the steady carriage of the body (as opposed to rotation of the body on its long axis).^ The radula (which is a rasping mouth part common to all molluscs) functions as a tongue, pulling in pieces of tissue torn off by the beak.
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^ Other special joints allow a cat to turn its head to reach most parts of its body.
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^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

.As a result, the Coelomata, and with them the Mollusca, present (in the first instance) the general condition of body known as bilateral symmetry; the dorsal is differentiated from the ventral surface, whilst a right and a left side similar to, or rather the complements of, one another are permanently established.^ Research in 2008 suggests another model, which hypothesizes the single opening shifts ventrally during the transition to bilateral symmetry with the anus fully formed only after protonephridia (which establishes a system of canals to expel watery waste, like the kidney in mammals) as indicated in Figure 08c.
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^ The relationship is not that clear in roundworm (protostomis), and the flatworm (nemertodermatida) still retains only one opening although it has bilateral symmetry.
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^ Snail (gastropod) Anatomy: Circulatory - The heart of the snail is found on the left side and consists of one auricle and one ventricle (Figure 11).
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.In common with all other Coelomata, the Mollusca have the mouth and first part of the alimentary canal which leads into the met-enteron formed by a special invagination of the outer layer of the primitive body-wall, not to be confounded with that which often, but not always, accompanies the antecedent formation of the archenteron; this invagination is termed the stomodaeum.^ The structure and function of the alimentary canal of some species of Polyplacophora (Mollusca).

^ Courtship, which in some species can be quite elaborate, is often a precursor to copulation.  Gonads are located in the posterior of the body.

^ A: he Cephlapods from which the octopi are a part of tend to eat crustaceans, other molluscs (cephlapods are from the phylum mollusca) and fishes.
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Similarly an anal aperture is formed in connexion with a special invagination which meets the hinder part of the met-enteron, and is termed the proctodaeum.
The coelom is primarily and essentially the generative cavity: the reproductive cells arise from its walls, i.e. from the coelomic epithelium. .True nephridia do not primarily open into the coelom, as was formerly taught, but are intra-cellular ducts in the mesoderm.^ Nephridia have two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall.
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^ In the Protobranchs and Filibranchs, the gonoducts opens directly into the nephridia and provide for the exit of sperm and eggs.

.Such organs are absent in Mollusca in the adult state, but a pair of nephridia usually occurs in the larva.^ Scaphopods possess a pair of nephridia (renal organs), which drain out of the body through nephridiopores located near the anus.  .

^ The usual molluscan sense organs such as eyes, tentacle and nephridia are absent in Scaphopods.  They do however have the familiar cerebral, pleural, pedal, and visceral ganglia and their corresponding nerve chords common to most molluscs.  .

The coelom opens to the exterior by ducts which are primarily genital ducts by which the ova or sperms are discharged. These ducts, however, as well as the coelomic epithelium, may assume excretory functions. .In Mollusca the coelom is reduced and consists of two parts, the pericardial cavity which surrounds the heart, and the cavity of the gonads or generative organs.^ They all have two-part shells, hinged dorsally .  The head is greatly reduced in size and their foot is laterally compressed.

^ General body plan consists of head, trunk, two pairs of appendages, and postanal tail (but these structures are highly modified in many vertebrates and .
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^ In higher vertebrates, other parts of the skeleton serve as attachment for muscles and for protection of internal organs of the thoracic cavity and the abdomen.
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.There is usually one pair of coelomic ducts leading from the pericardium to the exterior, and these are the excretory organs or kidneys, formerly known as the organs of Bojanus.^ Excretory - The kidneys are important excretory and water-regulating organs that conserve or rid the body of water as appropriate.
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^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

The walls of the pericardium are also excretory in parts, these parts forming the pericardial glands. .In the majority of Mollusca the gonads are provided with a pair of ducts of their own.^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

There are thus two pairs of coelomic ducts. This fact gives rise to the question whether the Mollusca are to be regarded as primitively segmented animals or not. .In animals which exhibit typical segmentation or metamerism, such as segmented worms (Chaetopoda), each segment or metamere possesses its own coelomic cavity, a pair of coelomic ducts, and a pair of nephridia.^ Scaphopods possess a pair of nephridia (renal organs), which drain out of the body through nephridiopores located near the anus.  .

^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

^ Excretory - The excretory system consists of paired nephridia, or coiled tubules, in each segment.
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.The structure of the Mollusca in the greater number of cases agrees with the hypothesis that the primitive form was unsegmented, and therefore had but one pair of coelomic ducts and one pair of nephridia.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ Nephridia have two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall.
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^ In echinoderms and chordates, the coelom forms by outpocketing of the primitive gut.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

In existing forms the latter disappear in the adult. .In the most primitive forms of several classes there are no distinct genital ducts, the gonads when mature discharging into or through the kidneys.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

^ In some of the freshwater hermaphrodites, self - fertilization may actually occur in the genital ducts before the eggs are deposited into the suprabranchial chamber.

.Among the Gastropoda, in the Aspidobranchia, there is no genital duct, and the gonad opens into the right kidney; in the more modified forms the left kidney alone is functional, the right has been converted into the genital duct.^ Although pseudogenes are generally accepted as nonfunctional and therefore not transcribed, occasionally it has been shown that such pseudogenes can be transcribed [ 60 ]; however, there is no evidence of the functional relevance.
  • BioMed Central | Full text | Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

.Among the Lamellibranchia again the kidneys serve as genital ducts in the Protobranchia and some Filibranchia.^ In some of the freshwater hermaphrodites, self - fertilization may actually occur in the genital ducts before the eggs are deposited into the suprabranchial chamber.

In the higher forms the opening of the gonad is shifted more and more towards the external aperture of each kidney until finally it is situated on the external surface, and thus the gonad secondarily acquires an independent aperture. In the Scaphopoda there is no distinct genital duct, the relations are as in Aspidobranchia. .Among the Amphineura we find one pair of coelomic ducts in the Aplacophora, two pairs in the Chitons.^ Nephridia have two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall.
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^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

In the former the genital coelom and the pericardial coelom are continuous and the reproductive cells escape by the renal ducts. .In the Chitons or Polyplacophora, on the other hand, the two cavities are separate, and there are independent genital ducts.^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

^ There are also two types of circular muscles, one type contracts for slow swimming and the other contract for fast escape swimming.
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^ On the other hand, there are several characteristics that are common to both of these animals.
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.It is possible therefore to regard the latter condition as secondary, and to conclude that the separate genital ducts have been derived from the original single pair of coelomic ducts, as in Lamellibranchs.^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

The Cephalopoda, however, do not harmonize so well with this view. The earliest forms of this class geologically are the Nautiloidea. .Assuming that these ancestral forms resembled the existing Nautilus in their internal anatomy, they had two pairs of renal ducts and one pair of genital ducts, which would apparently indicate, not a single metamere or unsegmented body, but three metameres.^ Scaphopods possess a pair of nephridia (renal organs), which drain out of the body through nephridiopores located near the anus.  .

^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

^ Monoplacophorans possess a single ventricle and two auricles for circulating the blood per body segment.  The first pair of auricles receives the blood from the first four pair of gills.  The pericardium is paired and the heart lies between the two divisions.

.There are however only two pairs of branchiae.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ Running along the mantle gutter cavity on either side of the body are five or six pairs of gills, however, filaments only exist on one side of the gill axis.

^ However, the adjacent cilia still remained attached only by tufts of cilia.  Each gill was now composed of two lamellae and formed a tight mesh.

.The Dibranchia, with only one pair of branchiae, one pair of renal organs, and one pair of genital ducts, are much more recent, not appearing till the end of the Secondary epoch, and therefore must be regarded as descended from the Tetrabranchia.^ Scaphopods possess a pair of nephridia (renal organs), which drain out of the body through nephridiopores located near the anus.  .

^ As demonstrated in C. elegans , many of these genes have apparently functional alleles in one or more wild isolates and therefore are not pseudogenes.
  • BioMed Central | Full text | Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ An applicant must own at least a 25 percent share in the vessel that the permit would cover, and only one permit will be assigned to any vessel.
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.The latter are represented in the Upper Cambrian formations, together with Lamellibranchia and Gastropoda, and there are no earlier Molluscan fossils than these.^ The shell is absent and there is no fossil record to suggest that any members of the class ever had one.  .

Palaeontology therefore throws no light on the question whether the metameric or the unsegmented Mollusca were the earlier. The development of the Cephalopoda affords at present no better evidence that the metamerism is secondary. That of Nautilus, which would be most important in this inquiry, is unfortunately still unknown. .In the Dibranchia true nephridia have not been detected in the embryo, nor has it been shown that the genital ducts are derived from the renal tubes.^ The two nephridia (a kind of primitive kidney, responsible for renal function) are quite large, and extend anteriorly on each side of the body as long U-shaped tubes.

.On the other hand, there is no evidence that the forms which show no metamerism, such as the Gastropoda, are descended from metameric ancestors.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ There are no specialized sense organs such as eyespots or electrical or chemical sensors.

^ On the other hand, there are several characteristics that are common to both of these animals.
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.On the whole, then, the most probable conclusion is that the original ancestral form of the Mollusca was unsegmented, possessed one pair of true nephridia, and one pair of coelomic ducts whose function was to conduct the generative products to the exterior.^ Scaphopods possess a pair of nephridia (renal organs), which drain out of the body through nephridiopores located near the anus.  .

^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ The sexes are separate, and two pair of gonads are located in the middle of the body.  Each gonad is connected by a duct to one of the two pairs of nephridia (kidneys), which are located in the middle of the body.

.The chief types of Mollusca were already differentiated at the beginning of the geological record, and the metamerism which occurs in the Cephalopoda has been evolved within the limits of that class.^ Kk1: Kristensen, T.K.; Knudsen, J. 1983: A catalogue of the type specimens of Cephalopoda (Mollusca) in the Zoological Museum, University of Copenhagen.

External Characters

.The characteristic organs of Mollusca are the mantle and shell, the foot, the ctenidia and the radula, of which all but the last are external.^ They all have two-part shells, hinged dorsally .  The head is greatly reduced in size and their foot is laterally compressed.

^ Take along a guide to shells with a diagram, and see if you can identify all of the external parts of the snail.
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^ A. All shells of animals in the phylum mollusca (snails, oysters, clams, etc.
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.The original form was bilaterally symmetrical, and this symmetry is retained in all the classes except the Gastropoda.^ It is believed that the bilateral larva developed types which retained the original symmetry, .
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^ The relationship is not that clear in roundworm (protostomis), and the flatworm (nemertodermatida) still retains only one opening although it has bilateral symmetry.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Unlike the adult, the larva is bilaterally symmetrical, suggesting that the radial symmetry of the starfish is a secondary affair, assumed when the ancestors of these forms look up a sedentary existence.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.At the anterior end the head is differentiated; it bears the sense-organs, and contains the muscular pharynx within which is the radular apparatus.^ Respiratory - Vertebrates have muscular, perforated pharynx, which functions as a filter-feeding apparatus in protochordates.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The frog heart is the only organ contained within the coelom, which has its own protective covering.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Digestive - The head of a nematode has a few tiny sense organs, and a mouth opening into a muscular pharynx where food (mostly bacteria and detritus) is pulled in and crushed.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The rest of the body consists of the foot ventrally and the visceral mass dorsally.^ The bivalve body has become greatly lengthened dorsal-ventrally (i.e., it has been flattened), and this flattening, in combination with an overhang of the shell, creates an extensive mantle cavity.

^ Nervous and Sensory - The nervous system consists of an anterior, dorsal, ganglionic mass, or a brain, and a long ventral solid nerve cord with ganglionic swellings and lateral nerves in each segment.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The esophagus leaves the buccal mass and passes from the foot into the visceral mass within the shell to form a crop.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The foot is a muscular mass without cuticle or skeleton, excepting certain cuticular structures such as the byssus of Lamellibranchs and the operculum of Gastropods, which do not aid in locomotion.^ The typical foot of a gastropod is a large flat creeping sole similar to the foot design of the ancestral mollusc.  It has become adapted for locomotion over a variety of surfaces.  .

^ Monoplacophorans possess a foot, round in outline and not very muscular, which is responsible for locomotion.   The muscular action is similar to that of the polyplacophorans.  (Please refer to the Polyplacophora for info on this.

^ Foot : the strong, muscular portion used for locomotion.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The foot is usually the pnly organ of locomotion. .It corresponds to the ventral part of the body-wall in other animals.^ Other special joints allow a cat to turn its head to reach most parts of its body.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The other B.C. species, Octopus rubescens is a smaller animal, with a body length (not including arms) of up to 15 cm.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The animal that makes it is a kind of snail (Phylum Mollusca: Class Gastropoda), and the shell is part of its body.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The muscular tissue of the dorsal body-wall is much reduced and the integument here is thin and FIG. i.^ It was observed in Mytilus galloprovincialis populations grown in the presence of NikkomycinZ that the growth rate of the larval shell is reduced relative to the growth rate of the body tissue.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ Gills are composed of vascularized, highly convoluted, thin-walled tissue specialized for gas exchange.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

- Ctenidia of various Mollusca (original).
.A, Of Chiton: f.t., fibrous tissue; a.b.v., afferent blood-vessel; e.b.v., efferent blood-vessel; g.l., laterally paired lamellae.^ Hemoglobin-containing blood moves anteriorly in a dorsal blood vessel and then is pumped by five pairs of hearts into a ventral blood vessel.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

B, Of Sepia: letters as in A.
C, Of Fissurella: letters as in A.
D, Of Nucula: d, position of axis with blood-vessels; a, inner: b and c, outer row of lamellae.
.E, Of Paludina: i, intestine running parallel with the axis of the ctenidium and ending in the anus a; br., rows of elongate processes corresponding to the two series of lamellae of the upper figures.^ The digestive system includes a mouth, a stomach, and an intestine, which coils about in the visceral mass and then goes right through the heart before ending in an anus (see Figure 10).
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Excretory - In mammals, the two major excretory processes are the formation of urine in the kidneys and the formation of feces in the intestines.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

G
q.t.
soft. The external epithelium of the dorsal region secretes the shell. .Between the edge of the shell and the foot there is a groove or cavity, chiefly developed laterally and posteriorly.^ In older stages of shell development, the influence of chitin synthase inhibition by NikkomycinZ is predominantly apparent at the shell's edge.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ They all have two-part shells, hinged dorsally .  The head is greatly reduced in size and their foot is laterally compressed.

^ They have no shell, but have calcareous spicules in the body surface.  The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body.

The dorsal border of this groove is extended outwards and downwards as a fold of the integument. .There is some confusion of terms here: some writers call the free fold the mantle or pallium, and this is the proper use of the term; but others apply the term to the whole of the dorsal integument, including both the projecting fold and the part covering the viscera.^ Usually calcium carbonate and other minerals are secreted into a protein matrix in the area that is called the mantle.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Both kinds of parthenogenesis occur most often in low-level species including some fish, amphibians and reptiles (see some examples in Figure 04d).
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ These chromatophores are under the control of the nervous system for the most part though there is also some hormonal control of the chromatophores as well.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The shell extends to the edge of the mantle-fold, and the cavity between the mantle and the side of the body is the pallial chamber.^ When the snail is extended, it covers almost the entire shell with its mantle (the outer edge of its body).
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The mantle cavity is the space between the two folds of the mantle.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ They live in the snail's body cavity and produce metacercariae that enter the mantle cavity ("lung") of the snail.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.This chamber serves two purposes: it is primarily 18 the respiratory cavity containing the gills, but it also serves to enclose the body so that the latter is surrounded by the shell, from which the head and foot can be protruded at the will of the animal.^ Respiratory - There are skin gills, which project from the coelomic cavity, serve the .
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ They all have two-part shells, hinged dorsally .  The head is greatly reduced in size and their foot is laterally compressed.

^ They have no shell, but have calcareous spicules in the body surface.  The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body.

.The shell consists of an organic basis the substance of which is called conchiolin, impregnated with carbonate of lime, with a small proportion, I-2%, of phosphate of lime.^ The shell is made up of three layers:  The periostracum or thin outer layer that is made of horny, organic material called conchiolin, the prismatic or thick middle layer that is made up of calcium carbonate crystals arranged in vertically, and the nacerous or thinner inner layer that is composed of thin horizontally arranged calcium carbonate crystals.  ( Diagram ) .

^ The layers may incorporate a substance called "conchin", often in order to help bind the calcium carbonate crystals together.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Almost no birefringence was observed in a 2 day old organism, which is consistent with a high fraction of amorphous calcium carbonate in the shell (Prodissoconch I).
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

.On the outside of the shell is a non-calcified layer of conchiolin called the periostracum, secreted by the thickened edge of the mantle.^ The mantle may secrete a shell.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The shell is made up of three layers:  The periostracum or thin outer layer that is made of horny, organic material called conchiolin, the prismatic or thick middle layer that is made up of calcium carbonate crystals arranged in vertically, and the nacerous or thinner inner layer that is composed of thin horizontally arranged calcium carbonate crystals.  ( Diagram ) .

^ This class also constructs its own shells, using the mantle tissue to build layer upon layer of shell material as the animal grows.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The zone of the external surface of the mantle within the edge secretes a layer formed of prisms of calcite; the rest of the epithelium from this zone to the apex secretes the inner layer of the shell, composed of successive laminae; this is the nacreous layer, and in certain species has a commercial value as nacre or mother-of-pearl.^ Inner surface layer – lateral growth and thickening of the larval shell .
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ The mantle may secrete a shell.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Musculo-skeletal - In a clam, the shell is secreted by the mantle and is composed of calcium carbonate with an inner layer of mother-of-pearl .
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.Thus the growth of the shell in extent is due to additions to the prismatic layer at the edge, its growth in thickness to new layers of nacre deposited on its inner surface.^ Inner surface layer – lateral growth and thickening of the larval shell .
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ The nacreous layer in the shells of the gastropod family Seguenziidae and its taxonomic significance.

^ "Rosette-like" structures as shown here were found distributed all over the inner shell surface of a 22 day old larva that had been treated with 10 μ M NikkomycinZ for 10 days.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

.In many cases in various classes the mantle is reflected over the edges of the shell, so as to cover more or less completely its outer surface.^ When the snail is extended, it covers almost the entire shell with its mantle (the outer edge of its body).
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Mantle : the membranous or sometimes muscular covering that envelops but does not completely enclose the visceral mass.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The anus opens into the mantle cavity near the edge of the mantle and the shell (see Figure 11).
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.When this covering is complete the shell is contained in a closed sac and is said to be " internal," but the sac is lined by ectoderm and the shell is always morphologically external.^ Each tooth spans the whole cross-section (thickness) of the shell's hinge throughout the complete line.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ A well-developed shell is covered by flakes (dotted lines) that consist of a granular material.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ The internal lumen of this "shell gland" is closed some hours after fertilization and the outmost cells start to secrete an organic shell cover, the periostracum, underneath a glycocalyx that originates from neighbouring cell microvilli.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

.In one or two cases the epithelium of the foot secretes a calcified shell, which is either free as in Argonauta or adherent as in Hipponyx. The ctenidia (fig.^ They all have two-part shells, hinged dorsally .  The head is greatly reduced in size and their foot is laterally compressed.

^ There are three classes of flatworms: one is free living and two are parasitic.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ These crabs did not make the shells that they live in - they simply found empty ones, or in some cases, killed and ate the original gastropod inhabitant.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

z) are the branchial organs of the Mollusca. .In the primitive condition there is one on each side in the mantle cavity, towards the posterior end of the body.^ They live in the snail's body cavity and produce metacercariae that enter the mantle cavity ("lung") of the snail.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Food particles and water enter the mantle cavity by way of the incurrent siphon (Figure 10), a posterior opening between the two valves.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.Each is an outgrowth of the body-wall at the side of the body, and consists of an axis containing two main vessels, an afferent and efferent, and bearing on either side a series of transverse plates whose blood-sinuses communicate with the vessels of the axis.^ Running along the mantle gutter cavity on either side of the body are five or six pairs of gills, however, filaments only exist on one side of the gill axis.

^ As the ventral blood vessel takes blood toward the posterior regions of the worm's body, it gives off branches in every segment.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Such a circulatory system is called an open circulatory system because the blood is not contained within blood vessels all the time.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The afferent vessel of the' ctenidium receives blood from the vena cava or principal blood-sinus of the body, the efferent vessel opens into the auricle of its own side.^ Such a circulatory system is called an open circulatory system because the blood is not contained within blood vessels all the time.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ There is also a lymphatic circulatory system of vessels and capillaries that transport lymph fluid through the bird's body and communicate with the blood supply.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ From the hemocoel blood passes into the veins and back to the auricle.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.Near the base of the ctenidium is a patch of sensory epithelium innervated from the branchial nerve, forming a sense-organ called the osphradium, whose function is to test the water entering the branchial cavity.^ Nervous and Sensory - Well-developed sense organs are needed for active animals.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Slow swimming: Water enters the mantle cavity by the expansion of the cavity due to a springing back of the collagen fibers (stretchy fibers) that extend along the mantle wall.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Food particles and water enter the mantle cavity by way of the incurrent siphon (Figure 10), a posterior opening between the two valves.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The branchial current is maintained by the cilia which cover the surface of the ctenidia, except in Cephalopoda, in which cilia are absent and the current is due to muscular action. .Thus in the primitive mollusc the mantle-cavity contains a symmetrical group of structures at the posterior end of the body, and this group of structures is called the pallial complex.^ They live in the snail's body cavity and produce metacercariae that enter the mantle cavity ("lung") of the snail.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Mollusc shells are made by a sheet of tissue called the mantle.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ This longer duct (pallial) leads directly to an opening in the mantle cavity.  .

.It consists of the anus in the middle, a renal organ and renal aperture on each side of this, and a ctenidium outside or anterior to the renal organ, an osphradium being situated at the base of the ctenidium.^ Scaphopods possess a pair of nephridia (renal organs), which drain out of the body through nephridiopores located near the anus.  .

^ The renal aperture (urine opening) is situated in the upper region of the right mantle cavity.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The organ consists of a series of interconnecting canals, which run the length of the body on each side.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

Internal Anatomy: Digestive Tube

.In primitive Mollusca the mouth and anus are the two extremities of the body, but the anus may be brought to an anterior position by a ventral flexure, complicated in Gastropoda by a lateral torsion.^ Nervous and Sensory - The nervous system consists of an anterior, dorsal, ganglionic mass, or a brain, and a long ventral solid nerve cord with ganglionic swellings and lateral nerves in each segment.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ They are soft-bodied animals with eight arms and two tentacles surrounding their mouth.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The pulmonates retained the post torsion anterior position of the anus and mantle cavity; however, the gills have disappeared and the mantle cavity has become modified into a lung .

.The alimentary tube consists of three regions: firstly, the anterior buccal mass with the oesophagus, of ectodermic origin, and therefore bearing cuticular structures, namely the jaws and radula; secondly, the mid-gut, of endodermic origin and including the stomach and liver; and, thirdly, the hind-gut or intestine.^ Observations on the structure and function of the buccal mass of Planorbarlus corneus (L.).

^ It consists of the gastrointestinal tract (gut), an extensive tube extending from the mouth to the anus, through which the swallowing, digestion, and assimilation of food and the elimination of waste products are accomplished.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The nervous system consists of an anterior, dorsal, ganglionic mass, or a brain, and a long ventral solid nerve cord with ganglionic swellings and lateral nerves in each segment.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The radula consists of a chitinous band bearing teeth, secreted by a ventral caecum of the pharnyx and moved by an apparatus of cartilage and muscles.^ In the gastropods ("belly-footed"), such as snail, the foot is ventrally flattened, and the animal moves by muscle contractions that pass along the foot.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.It was present in the ancestral mollusc, occurs in nearly all archaic types, and is only absent in the most specialized forms, in which it has evidently been lost; these forms are certain Neomeniomorpha, all the Lamellibranchia, various degenerate Gastropoda, and the Cirrhoteuthidae among Cephalopods.^ Cephalopods are thought to be the most intelligent of all molluscs and possibly of all invertebrates.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Cephalopods molluscs (octopus and their relatives) eat all sorts of animals, from fish to crabs.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ While all clams have some type of larval stage, only marine clams have a trochohore larva.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The teeth are secreted by a small number of cells at the closed end of the caecum, the basal membrane by a transverse row of cells in front of these.^ The close-up view of the small hinge teeth (Fig.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ By the end of cleavage these cells generally form a fluid-filled sphere known as blastula.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The teeth are disposed in transverse rows, and in each row they are arranged symmetrically on either side of a central tooth. .In Polyplacophora there are eight on each side (8.I.8); in Scaphopoda two on each side (2.I.2); in almost all Cephalopoda three on each side (3.I.3); in Gastropoda the number varies very much in different subdivisions.^ Almost all animal species reproduce sexually, which is believed to have evolved as a mean of strengthening the "fitness" of the species by mixing the genes of two different individuals from meiosis .
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Two limestone 'islands' in central northern Greece, six new clausiliid taxa, three kinds of microarmature (Gastropoda, Pulmonata, Clausiliidae).
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

^ There are many other features that all Cephalopoda have in common.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.Beneath the anterior parts of the radula where it emerges from the caecum are a pair of cartilages, and attached to these a number of special muscles by which the radula is moved backwards and forwards to act as a rasp.^ The radula (which is a rasping mouth part common to all molluscs) functions as a tongue, pulling in pieces of tissue torn off by the beak.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ These squid have a special organ on their backs that they use to attach themselves to seaweed.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ When the funnel is directed backwards the fastest swimming in achieved when the squid move forward.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The secretion of the radula at the closed end of the caecum is continuous, so that it is constantly growing forward as fast as its exposed anterior portion is worn away by use, just as a fingernail is pushed forward by constant growth at its posterior end, and is worn away or has to be cut short from time to time at its outer end.^ It wears away with use, but is continuously replaced since it is formed in a radular sac at the end of the buccal mass and grows constantly, like the human fingernail.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

Circulation

.The system of blood-vessels is entirely separate from the coelomic cavities.^ Such a circulatory system is called an open circulatory system because the blood is not contained within blood vessels all the time.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ There is also a lymphatic circulatory system of vessels and capillaries that transport lymph fluid through the bird's body and communicate with the blood supply.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Circulatory - All vertebrates have a closed circulatory system in which red blood is contained entirely within blood vessels.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

It consists of arteries, veins and sinuses, but ramified capillaries are usually absent except in the integuments of Cephalopods. .The arteries and veins have proper endothelial walls; they pass abruptly into the sinuses and in some cases communication is effected by orifices in the walls of the vessels, as for example in the vena cava of Nautilus. The heart is situated in the pericardium on the dorsal side of the intestine and at the posterior end of the animal.^ Solid wastes from the large intestine pass into the cloaca.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Behind the crop is a dilated stomach, which is followed by the long intestine, whose posterior end is dilated to form the rectum.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ These crabs did not make the shells that they live in - they simply found empty ones, or in some cases, killed and ate the original gastropod inhabitant.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The pericardium never contains blood, as is well shown in those forms wl.ich have red corpuscles in their blood; these corpuscles are never found in the pericardium.^ The spaces between the trabeculae are filled with red bone marrow containing the blood vessels that nourish spongy bone.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ These capsular proteins form long fibers with well-defined alpha helical conformations that are packed into ribbon-like units.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Circulatory - All vertebrates have a closed circulatory system in which red blood is contained entirely within blood vessels.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The heart receives blood from the gills and mantle, and pumps it through arteries to the body.^ There is a heart at the end of each of their gills; these hearts pump blood through the gills.
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^ The third heart pumps blood through the rest of the body.
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^ One or more renal arteries can be present to receive blood from the renal portal system.
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It consists of a median ventricle with muscular walls and a cavity traversed by muscular strands. .On either side of the ventricle, in the primitive condition, is a thinwalled auricle, opening into the ventricle by a valved opening.^ Snail (gastropod) Anatomy: Circulatory - The heart of the snail is found on the left side and consists of one auricle and one ventricle (Figure 11).
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Each auricle forms the terminal enlargement of the efferent vein of the ctenidium of its own side. In Nautilus two pairs of auricles are present, corresponding with the two pairs of ctenidia. .In the primitive form a single anterior aorta is given off from the ventricle, the two together representing the dorsal blood-vessel of Chaetopods.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ The right atrium receives impure blood with little oxygen from the body proper, and the left atrium receives purified blood from the lungs that has just been oxygenated, but these two types of blood are mixed partially in the single ventricle.
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^ As the water passes over the gills, oxygen is absorbed by blood and carbon dioxide is given off.
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.In more specialized forms a posterior aorta passes backwards from the ventricle, as in Gastropods and the majority of Lamellibranchs.^ On the origin and evolution of major gastropod groups, with special reference to the Streptoneura.

.The ramifications of the arteries convey the blood to all parts of the body, and it finally reaches the venous sinuses, the chief of which are the pedal, the pallial and the median-ventral.^ Other special joints allow a cat to turn its head to reach most parts of its body.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The systemic circuit carries oxygenated blood to all the body's cells via arteries, and deoxygenated blood back to the heart via veins.
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^ As the ventral blood vessel takes blood toward the posterior regions of the worm's body, it gives off branches in every segment.
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.The last is between the pericardium and the foot; from it the blood passes through the renal organs to the ctenidia.^ Within the organs, however, blood flows through spaces, or sinuses , rather than through vessels.
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.Some blood, however, enters the auricles directly from the mantle, without passing through the ctenidia.^ Within the organs, however, blood flows through spaces, or sinuses , rather than through vessels.
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^ From the hemocoel blood passes into the veins and back to the auricle.
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^ Their mantle is richly supplied with blood vessels and functions as a lung when air is moved in and out through respiratory pores (Figure 11).
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In the majority of Gastropoda one gill and one auricle are lost.
.The blood is usually a colourless liquid containing amoeboid cells and sometimes other corpuscles called haematids.^ It also ensures that the mother's immune system does not attack the embryo by separating white blood cells and other immune system components (including blood) at the boundary.
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^ All the other cells of the body are called somatic cells.
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^ Usually calcium carbonate and other minerals are secreted into a protein matrix in the area that is called the mantle.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.It may be coloured blue by haemocyanin, a respiratory compound containing copper.^ Some shells may also contain pigments, which accounts for the fabulous colours of some sea shells.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ These chromatophores may be one of several colours: yellow, orange, red, blue or black.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.In a few forms the blood contains haemoglobin, either in solution or in haematids (red blood-corpuscles).^ The heart pumps blue blood, containing the pigment hemocyanin instead of red hemoglobin, into vessels that lead to the various organs of the body.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The spaces between the trabeculae are filled with red bone marrow containing the blood vessels that nourish spongy bone.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Circulatory - All vertebrates have a closed circulatory system in which red blood is contained entirely within blood vessels.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

In the Gastropoda the muscular tissue of the buccal mass is coloured red by haemoglobin.

Nervous System

.The central nervous system may be described as consisting of a collar surrounding the oesophagus, and two pairs of cords arising from the collar and passing backwards.^ Nervous and Sensory - The greater portion of the gastropod nervous system, called the brain, consists of nine large ganglia, eight of which are paired.
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^ General body plan consists of head, trunk, two pairs of appendages, and postanal tail (but these structures are highly modified in many vertebrates and .
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^ Further, the two systems interact closely and control each other so that endocrine organs may be the target of the CNS and vice versa.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.The two pairs of cords arise from the same point of the collar.^ If two or more owners have the same number of points and there are insufficient permits for all such owners, the Regional Administrator shall issue the permits through a lottery.
  • Justia Regulation Tracker Western Pacific Fisheries; Regulatory Restructuring , - National Oceanic and Atmospheric Administration - 2198–2268 [E9–30972] 17 January 2010 1:54 UTC regulations.justia.com [Source type: FILTERED WITH BAYES]

.The ventral cords are the pedal, the dorso-lateral, the pleural, the former innervating the foot, the latter the mantle.^ This soft and delicate capsule is then transferred via a temporary groove in the anterior portion of the female's foot to a deep gland in the base of her foot known as the ventral pedal gland.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The nervous system consists of an anterior, dorsal, ganglionic mass, or a brain, and a long ventral solid nerve cord with ganglionic swellings and lateral nerves in each segment.
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^ When invertebrates are compared to vertebrates, it often is said that the former have a ventral solid nerve cord, while the latter have a dorsal hollow nerve cord.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The dorsal half of the collar is the cerebral commissure, the ventral the labial commissure. The pedal cords are connected by commissures, and the pedal and pleural of each side are similarly connected. The pallial cords are united to one another posteriorly, dorsal to the rectum. .This is the condition of the nervous system found in Chiton and the other Amphineura, but may not be in all respects the ancestral condition.^ Permit Area X-P-G includes all coral beds, other than established beds, conditional beds, or refugia, in the EEZ seaward of Guam.
  • Justia Regulation Tracker Western Pacific Fisheries; Regulatory Restructuring , - National Oceanic and Atmospheric Administration - 2198–2268 [E9–30972] 17 January 2010 1:54 UTC regulations.justia.com [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ All these functions can be found in the Human Organ Systems as shown in Figure 01a or in Table 10-01, Topic 10 .
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.Generally the system is differentiated into ganglia connected by nerve-cords consisting of nerve-fibres only.^ Nervous and Sensory - The greater portion of the gastropod nervous system, called the brain, consists of nine large ganglia, eight of which are paired.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The nervous system consists of a central nerve ring that supplies radial nerves to each arm.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.At the point of the collar whence the nerve-cords arise are the cerebral ganglia; from these one pair of connectives passes to a pair of pedal ganglia, and another pair of connectives to a pair of pleural ganglia.^ Large branching nerves originating in these ganglia innervate all parts of the body, while several small ganglia are associated with sense organs.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
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^ These animals belong to the classes Chilopoda (see Figure 15C) and Diplopoda (it has 2 segments fused into one - 2 pairs of legs for each segment).
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.Pedal and pleural on each side are connected by a pleuro-pedal connective Each pleural ganglion gives off a long nerve which supplies the viscera, and the two unite posteriorly below the intestine.^ Nervous and Sensory - The muscles are activated by two nerves that run the length of the nematode on both the dorsal and ventral side.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The nervous system consists of an anterior, dorsal, ganglionic mass, or a brain, and a long ventral solid nerve cord with ganglionic swellings and lateral nerves in each segment.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The stomach has two portions: the saclike cardiac, which can be everted as described, and the narrower pyloric, which is connected to a short intestine.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

.There are usually three small ganglia on the course of this visceral commissure, namely, the right and left visceral ganglia and the abdominal.^ A: Common names for animals usually tend to be a bit ambiguous, since there are many different species of clams which could be known as the soft clam.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The perioesophageal nerve-ring of Chaetopoda and Arthropoda is represented, not by the collar first mentioned in the above description, but by the commissures connecting the cerebral and pedal ganglia.^ The ventral nerve has a series of nerve centers along its length, and both nerves connect to a nerve ring and additional nerve centers located near the head (see Figure 08b).
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The labial commissure supplies only the buccal mass and the oesophagus and stomach.
The special sense-organs are a pair of eyes on the head, a pair of otocysts or statocysts, and a pair of osphradia which have already been mentioned. In certain cases accessory eyes are also present, e.g. the pallial eyes of Pecten and other Lamellibranchs, and of Chitons. The otocysts are invaginations of the epithelium of the foot, but are innervated from the cerebral ganglia, and the same innervation has been proved in some cases for the osphradia.

Reproduction and Development

.Molluscs are usually of separate sexes, but sexual dimorphism is seldom highly developed.^ Sexual reproduction can be either hermaphroditic (organism having both sexes) or gonochoristic (separate sexes).
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.Hermaphroditism is secondary, and occurs in one sub-class of Gastropoda, in some Lamellibranchs, and in one sub-order of Amphineura.^ One subgroup in this phylum is the class Gastropoda.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

In Cephalopods and the majority of Gastropods copulation occurs. .As a rule no parental care is exhibited, but incubation of the developing ova within some part of the parental body, or receptacles attached to the parent, occurs in some Lamellibranchs, some Gastropods, and in Argonauta among the Cephalopods.^ I was wondering if you could give me some information on its body parts and possibly a diagram?
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The shell characteristics are, for the most part, controlled by genetics, although there can be individual variation within a particular species (some more than others).
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ In some species, embryos spend only a short time developing within the capsule and then hatch out as larvae destined to spend the rest of their developmental period as part of the plankton.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.True viviparity, that is the development of the ova within the oviduct, is very rare, occurring only in one case among the Amphineura and in some aquatic and pulmonate Gastropoda.^ Following this, fertilized eggs and albumen are deposited within this secretion, and the capsule leaves the female's oviduct in the form of a soft pliable bag filled with developing embryos.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ We thought they were some garbage some one dropped, but a friend told us they were egg cases for some kind of creature.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ SEM samples) can be excluded, a possible explanation for some very rarely observed shell malformations in NikkomycinZ treated larva as shown in Fig.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

The egg-cell of Mollusca is either free from food-material - a simple protoplasmic corpuscle or charged with food-material to a greater or less extent. Those cases which appear to be most typical - i.e. which adhere to a procedure which was probably common at one time to all then existing Mollusca and has been departed from only in later and special lines of descent - show approximately the following history. .By division of the egg-cell a mulberry-mass of embryonic-cells is formed (morula), which dilates, forming a one-celllayered sac (blastula).^ Gastrulation - The cells in the blastula undergo dramatic movements wherein they change their positions relative to one another.
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^ By the end of cleavage these cells generally form a fluid-filled sphere known as blastula.
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^ In the early embryonic stages of mollusc development, differentiated ectodermal cells form the shell field, a tissue that excretes the larval shell, as reviewed by Kniprath [ 41 ].
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

.By invagination one portion of this sphere becomes tucked into the other - as in the preparation of a woven night-cap for the head.^ The worms practice cross-fertilization; the penis of one is inserted into the genital pore of the other.
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.The orifice of invagination (blastopore) narrows, and we now have a two-cell-layered sac - the gastrula.^ Two layers of cells .
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.The invaginated layer is the enteric cell-layer or endoderm; the outer cell-layer is the dermic cell-layer or ectoderm.^ The nerve net makes contact with the outer layer of cells, called the epidermis, and the inner layer of cells, called the gastrodermis.
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^ The outer layer of the sac, the ectoderm, is separated from the inner layer, the endoderm, by a jellylike material called mesoglea (see Figure 05a).
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The cavity communicating with the blastopore and lined by the endoderm is the archenteron. The blastopore, together with the whole embryo, now elongates. The blastopore then closes along the middle portion of its extent, which corresponds with the later developed foot. At the same time the stomodaeum, or oral invagination, forms around; the anterior remnant of the blastopore, and the proctodaeum, or anal invagination, forms around the posterior remnant of the blastopore. There are, however, variations in regard to the relation of the blastopore to the mouth and to the anus which are probably modifications of the original process described above.
.In eggs which contain a larger quantity of food-yolk, the process by which the endoderm is enveloped by the ectoderm is somewhat different.^ Food in the mouth is mixed with saliva, which contains enzymes that begin the process of digestion.
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.Segmentation in these is very unequal, and results in the formation of small cells called micromeres and large cells called megameres, as in fig.^ The very small chance of fertilization is compensated by the enormous amounts of eggs and sperm cells.
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^ Cleavage is meroblastic, and results in the formation of a germinal disc of cells at the animal pole where the embryo forms.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ These results indicate a direct interference of NikkomycinZ with the formation and remodelling of hinge teeth in the bivalve larvae of Mytilus galloprovincialis throughout development.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

4. As the micromeres become more numerous they gradually envelop the megameres until the latter are completely enclosed. The gastrula is in these cases said to be formed by epibole. .Between ectoderm and endoderm a third intermediate cell-layer _r B (After Lankester, 15.) FIG. 2. - Development of the Pond-Snail, Limnaeus stagnalis. r, Directive corpuscle.^ Whole-body enantiomorphy and maternal inheritance of chiral reversal in the pond snail Lymnaea stagnalis .
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

^ The outer layer of the sac, the ectoderm, is separated from the inner layer, the endoderm, by a jellylike material called mesoglea (see Figure 05a).
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A, First four cells resulting from bl, Blastopore. the cleavage of the original en, Endoderm or enteric cell layer. egg-cell.
ec, Ectoderm or deric cell-layer. B, Side-view of the same.
v, Velum. C, Diblastula stage showing the m, Mouth. two cell-layers and the f, Foot. blastopore.
1, Tentacles. .D, E, F, Trochosphere stage, D fp, Pore in the foot (belonging mf, The mantle-flap or limbus to the pedal gland?^ This soft and delicate capsule is then transferred via a temporary groove in the anterior portion of the female's foot to a deep gland in the base of her foot known as the ventral pedal gland.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The pedal gland at front end of the foot secretes a thin, flat ribbon of mucus for the snail to move along.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

). G, Three-quarter view of a Dibolder than E or F.
lastula, to show the orifice of invagination of the endo pallialis. derm or blastopore, (bl).
sh, The shell.
.H, I, Veliger stage later than 1, The sub-pallial space, here destined to become the lung.^ The notochord in vertebrates breaks up in later stage and ultimately becomes part of the disks that lie between the vertebrae.
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^ In later developmental stages the inner surface of larval shells is usually smooth, homogeneous, compact, and the shell flakes are more confluent than in the younger developmental stage.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

D.
is formed, which is called the mesoderm, and gives rise to the muscular and .connective tissues to the vascular system, and to the excretory and generative organs.^ The more complex animals have organ systems to carry out these functions; in simple animals, these functions sometimes are carried out by specialized tissues.
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^ Metamorphosis is a critical time of transition when increased concentrations of metamorphic hormones orchestrate the loss or reorganization of many tissues and organ systems, including the immune system.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The mesoderm arises for the most part from the endoderm. .When the segmentation is unequal one of the megameres gives rise by successive divisions to two primary mesoderm cells called mesomeres; these divide to form two masses of cells called mesoblastic bands.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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^ At one time, both body forms may have been a part of the life cycle of all cnidarians, because today we see an alternation of generations life cycle of these two forms in certain cnidarians (see Figure 05d).
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^ These two forms are free swimming, are found in the plankton, and do not look much like the adult clam.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The coelom is formed as a cavity or cavities in the interior of these cell-masses.^ By the end of cleavage these cells generally form a fluid-filled sphere known as blastula.
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In some cases the coelom is formed as a single cavity, and renal and generative organs are formed from its walls. .This is the primitive method, but in other cases the organs mentioned may be formed separately in the mesoderm.^ Further, the two systems interact closely and control each other so that endocrine organs may be the target of the CNS and vice versa.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ The principal responsibility of the organ is to separate urea, toxins, and other types of waste from the blood, while water, salt, and electrolytes are maintained at an appropriate level.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

The renal organs are tubular outgrowths of the pericardial parts of the coelom; the reproductive cells are derived from cells lining the generative portion.
.The external form of the embryo meanwhile passes through highly characteristic changes, which are on the whole fairly constant ara (After Lankester, 17.) FIG. 3. - Development of the River-Snail, Paludina vivipara. Gastrula phase (optical section).^ Following this, fertilized eggs and albumen are deposited within this secretion, and the capsule leaves the female's oviduct in the form of a soft pliable bag filled with developing embryos.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Among the more highly developed snails fertilization takes place internally in the female or at least in the snail acting as female.
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

^ Vertebrae develop from segments of tissue called somites, which form, one after another, in a head-to-tail sequence in the embryo (diagram a, Figure 19e).
  • Anatomy of Animals 17 January 2010 1:54 UTC universe-review.ca [Source type: FILTERED WITH BAYES]

B, The Gastrula has become a Trochosphere by the development of the ciliated ring vr (optical section).
C, Side view of the Trochosphere with commencing formation of the foot.
D, Further advanced Trochosphere (optical section).
.E, The Trochosphere passing to the Veliger stage, dorsal view showing the formation of the primitive shell-sac.^ Note that the larvae are already in the early veliger stage and have a D-shaped shell.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ Note that the size of the shell increased, and the larvae switched from the D-shape stage to the umbo stage of shell formation.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

^ The shell of this trochophora larval stage, the prodissoconch I, is enlarged until the entire embryo is covered, and the organism metamorphoses into the motile veliger larva.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

.F, Side view of the same, showing foot, shell-sac (shgl), velum (vr), mouth and anus.^ Figure 08c Evolution of Mouth and Anus [view large image] .
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N.B. - In this development the blastopore is not elongated; it persists as the anus. The mouth and stomodaeum form independently of the blastopore.
throughout the Mollusca. A circlet of cilia forms when the embryo is still nearly spherical in an equatorial position. As growth proceeds, one hemisphere remains relatively small, the other elongates and enlarges. .Both mouth and anus are placed in the larger area; the smaller area is the prostomium simply; the ciliated band is therefore in front of the mouth.^ These animals possess a single digestive opening served as both mouth and anus.
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The larval form thus produced is known as the trochosphere. .It exactly agrees with the larval form of many Chaetopod worms and other Coelomata.^ In other species (including many worms and most mammals) the egg nucleus is still diploid and the sperm enters before the meiotic divisions are completed.
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Most remarkable is its resemblance to the adult form of the Wheel animalcules, or Rotifera, which retain the prae-oral ciliated band as their chief organ of locomotion and prehension throughout life. So far the young mollusc has not reached a definitely molluscan stage of Xviji. 22 dc, Directive corpuscle (outcast cell).
ae, Arch-enteron or cavity lined by the enteric cell-layer or endoderm.
bl, Blastopore.
vr, Velum or circlet of ciliated cells.
dv, Velar area or cephalic dome. sm, Site of the as yet unformed mouth.
f, Foot.
mes, Rudiments of the skeletotrophic tissues.
pi, The pedicle of invagination, the future rectum.
shgl, The primitive shell-sac or shell-gland.
m, Mouth. an, anus.
A, development, being only in a condition common to it and other Coelomata. .It now passes to the veliger phase, a definitely molluscan form, in which the disproportion between the area in front of the ciliated circlet and that behind it is very greatly increased, so that the former is now simply an emarginated region of the head fringed with cilia.^ Close-up view of the transition region as indicated by an arrow in (g) between the earlier and recently formed hinge teeth.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

It is termed the " velum," and is frequently drawn out (From Balfour, after Bobretzky.) .FIG. 4. - Early Stages of division of the Fertilized Egg-cell in Nassa mutabilis. A, The egg-cell has divided into two spheres, of which the lower contains more food-material, whilst the upper is again incompletely divided into two smaller spheres.^ Fertilization is the process whereby two sex cells (gametes) fuse together to create a new individual with genetic potentials derived from both parents.
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^ The lifecycle of most starfishes starts by shedding their eggs and sperm freely into the water, so fertilization is externally.
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^ The very small chance of fertilization is compensated by the enormous amounts of eggs and sperm cells.
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.Resting on the dividing upper sphere are the eight-shaped " directive corpuscles," better called " praeseminal outcast cells or apoblasts," since they are the result of a cell-division which affects the egg-cell before it is impregnated, and are mere refuse, destined to disappear.^ But they have specialized stinging cells called cnidocytes, from a Greek word meaning sea nettles.
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^ In other species (including many worms and most mammals) the egg nucleus is still diploid and the sperm enters before the meiotic divisions are completed.
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^ These cells are called germ cells, and they are set aside for their reproductive function.
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B, 0.1e of the two smaller spheres is reunited to the larger sphere.
C, The single small sphere has divided into two, and the reunited mass has divided into two, of which one is oblong and practically double, as in B.
D, Each of the four segment-cells gives rise by division to a small pellucid cell.
.E, The cap of small cells has increased in number by repeated formation of pellucid cells in the same way, and by division of those first formed.^ Cleavage is meroblastic, and results in the formation of a germinal disc of cells at the animal pole where the embryo forms.
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^ Cephalopods such as cuttlefish, squid and octopuses have eyes that are similar to those of vertebrates like humans (with small variation in the orientation of the retinal cells).
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The cap will spread over and enclose the four segment-cells.
into lobes and processes. As in the Rotifera, it serves the veliger larva as an organ of locomotion. .The body of the veliger is characterized by the development of the visceral hump on one surface, and by that of the foot on the other.^ Nephridia have two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall.
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.Growth is greater in the vertical dorso-ventral axis than in the longitudinal oro-anal axis; consequently the foot is relatively small and projects as a blunt process between mouth and anus, which are not widely distant from one another, whilst the antipedal area projects in the form of a great hump or dome.^ Gastrulation - The cells in the blastula undergo dramatic movements wherein they change their positions relative to one another.
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^ Vertebrae develop from segments of tissue called somites, which form, one after another, in a head-to-tail sequence in the embryo (diagram a, Figure 19e).
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^ In deuterostomes (secondary mouth) the site of gastrulation (the site at which the endomesoderm forms) becomes the anus and the mouth is formed at a different end.
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.In the centre of this antipedal area there has appeared (often at a very early period) a gland-like depression or follicle of the integument.^ It burrows into muddy and sandy areas, often around mussel beds and in areas where there are likely to be clams.
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.This is the primitive shell-sac discovered by Lankester in 1871, and shown by him to precede the development of the permanent shell in a variety of molluscan types.^ Throughout the animal kingdom an incredible variety of embryonic types exists, but most patterns of embryogenesis comprise variations on four themes as shown by the development of a representative organism, the frog, in Figure 19f: .
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^ A scanning electron microscopy image of a well developed, 19-day shell reared under the conditions of the test without NikkomycinZ is shown in Fig.
  • BioMed Central | Full text | The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z 9 January 2010 13:35 UTC www.biomedcentral.com [Source type: Academic]

The shell-gland is bounded by a ridge of ectodermic cells. .This ridge forms the edge of the shell-secreting epithelium, and therefore of the mantle, since the shell extends to the edge of the mantle.^ The mantle may secrete a shell.
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^ The anus opens into the mantle cavity near the edge of the mantle and the shell (see Figure 11).
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^ As the snail grows it secretes a substance around part of its body which hardens to form the shell.
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The shell-gland, as development proceeds, extends from its point of origin as an ectodermic thickening, which may be only slightly concave or may be deeply invaginated and then evaginated.
In the larvae of several Gastropoda and Lamellibranchia occur excretory organs which have the characters of true nephridia. There is a single pair of these organs situated immediately behind the velum. They agree with primitive nephridia in being of ectodermic origin, in consisting of perforated cells in linear series, and in having no communication with the coelom. .The inner end of each of these organs consists of a flame-cell, i.e. a cell with an internal cavity containing a vibrating filament or flagellum.^ These cells contain contractile fibers.
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^ In higher vertebrates, other parts of the skeleton serve as attachment for muscles and for protection of internal organs of the thoracic cavity and the abdomen.
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^ By the end of cleavage these cells generally form a fluid-filled sphere known as blastula.
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.They are best developed in the Pulmonata; in some cases they are very rudimentary and may be destitute of an external opening.^ They have external ear openings and their eyes have movable eyelids (unlike snakes).
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^ Comparing gene sequences (with other animals) suggests that they may be very close to the "Animal Eve" called urmetazoan .
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^ The scales may be smooth or they may have little ridges called keels or they may even have developed into spines.
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.They invariably disappear before the adult stage is reached, but their presence in the larva is evidence that the ancestral mollusc possessed a pair of true nephridia quite distinct from the coelomic excretory organs, which are so characteristic of existing forms in the adult condition.^ Excretory - The excretory system consists of paired nephridia, or coiled tubules, in each segment.
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^ Excretory - Excretory functions are carried out by a pair of nephridia (kidneys), tubular structures that collect fluids from the coelom and exchange salts and other substances with body tissues as the fluid passes along the tubules for excretion.
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^ They have an excretory organ that largely rids the body of excess water.
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The ctenidia, it will be observed, have not yet been mentioned, and they are indeed the last of the characteristic Molluscan organs to make their appearance. .They arise as outgrowths of the sides of the body within the cavity formed by the development of the mantle.^ Rather, they arise by a relatively slow process of progressive change that is called development .
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^ They live in the snail's body cavity and produce metacercariae that enter the mantle cavity ("lung") of the snail.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Following this, fertilized eggs and albumen are deposited within this secretion, and the capsule leaves the female's oviduct in the form of a soft pliable bag filled with developing embryos.
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.The veliger, as soon as its shell has attained some extent and begins to assume definite shape, is no longer of a form common to Mollusca generally, but acquires characters peculiar to the partiY cular class to which its parents belong.^ Larval shell morphology of some Japanese haliotids for the identification of their veliger larvae and early juveniles.

^ A permit holder who receives a Class B-1, C-1, or D-1 permit must relinquish his or her Class A permit and that permit will no longer be valid.
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^ Mn5: McLean, J. H.; Geiger, D.L. 1998: New genera and species having the Fissurisepta shell form, with a generic-level phylogenetic analysis (Gastropoda: Fissurellidae).

For the later development therefore the articles on the several classes must be consulted.

Relations between the Classes

From the preceding discussion an idea may be formed of the primitive characters of the Phylum (From Gegenbaur.) FIG. 5. - " Veliger " embryonic form of Mollusca.
v, Velum. A, Earlier, and (B), later, Veliger c, Visceral dome with dependent of a Gastropod.
mantle-skirt. C, Veliger of a Pteropod showing p, Foot. lobe-like processes of the t, Cephalic tentacles. velum and the great paired op, Operculum. outgrowths of the foot.
.Mollusca, and it is possible to construct a diagrammatic mollusc, as was first done by Lankester, which will possess these primitive features.^ Roundworms possess two anatomical features not seen in more primitive animals: a tube-within-a-tube body plan and a body cavity.
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.The figure here given represents such a hypothetical form according to present views.^ Excretory - There are two kidneys (Figure 11), or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost.
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.We cannot assert that this was in all respects the condition of the common ancestor, as will be seen when we attempt to derive the various sub-types from it.^ Humans, bats, lizards, and whales are all just variations on a theme (see for example the common pattern of limbs for some vertebrates in Figure 19c).
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In the Amphineura the nervous system, having no (From Lankester's Treatise on Zoology. A. and C. Black.) FIG. 6. - Diagram of a primitive Mollusc, viewed from the left side.
a, Anus. pa.n, Pallial nerve.
cg, Cerebral ganglion. pe, Pericardium.
f, Foot.
g, Gill, in the pallial cavity. pl.g, Pleural ganglion. p.g, Pedal ganglion.
ra, Radula.
go, Gonad. r.p.o, Reno-pericardial orifice.
h, Heart.
st, Stomach.
k, Kidney. st.g, Stomato-gastric ganglion. la.c, Labial commissure.
v.g, Visceral ganglion.
m., Mouth.
pa, Mantle.
separate ganglia and n6 ventral visceral commissure, may be still more primitive. .The metameric repetition of the shellplates and of the ctenidia are probably special modifications, but it is difficult to explain the spicules of the dorsal integument except as a condition more primitive than the shell itself.^ While human has only 33, snakes have more than 300, with some species having more than 500.
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^ The shell characteristics are, for the most part, controlled by genetics, although there can be individual variation within a particular species (some more than others).
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ On average then, an adult giant squid will probably have to eat more than an adult Octopus vulgaris.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

The Prorhipidoglossomorpha are distinguished by the separation of the genital coelom from the pericardium, and by the long visceral commissure passing ventral to the intestine. The Lamellibranchia have markedly diverged from the original type by the adoption of filtration as a method of feeding. .This has led to the loss of the radula, and is accompanied by the division of the shell into two valves.^ The clam has two calcareous valves which are commonly referred to as the shell, which protects the animal's soft parts.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.The peculiarities of the Gastropoda are all due to the torsion of the shell and body.^ The animal that makes it is a kind of snail (Phylum Mollusca: Class Gastropoda), and the shell is part of its body.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

The Cephalopoda can be derived without much difficulty from the schematic Mollusc, if we assume that some metameric repetition of organs has occurred, as explained above in reference to the coelom. .The foot has been developed into long processes which have extended in a circle round the mouth; all the ganglia, including the visceral, have been concentrated around the oesophagus.^ Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia (anterior, foot, and posterior, see Figure 10), which all are connected by nerves.
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^ The esophagus leaves the buccal mass and passes from the foot into the visceral mass within the shell to form a crop.
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^ After all appeals on initial permits are concluded in any vessel size class, the maximum number of permits in that class shall be the number of permits issued during the initial issuance process (including appeals).
  • Justia Regulation Tracker Western Pacific Fisheries; Regulatory Restructuring , - National Oceanic and Atmospheric Administration - 2198–2268 [E9–30972] 17 January 2010 1:54 UTC regulations.justia.com [Source type: FILTERED WITH BAYES]

Habits and Distribution

.More than 28,000 species of living Molluscs have been distinguished, of which more than half are Gastropods.^ While human has only 33, snakes have more than 300, with some species having more than 500.
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^ The shell characteristics are, for the most part, controlled by genetics, although there can be individual variation within a particular species (some more than others).
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

They are essentially aquatic animals, and the h, Heart, in the pericardium. h.a, Posterior adductor.
m, Mouth.
pa, Pallium or mantle.
p.g, Pedal ganglion.
pl.g, Pleural ganglion.
ra, Radula.
st, Stomach.
st.g, Stomato-gastric ganglion. v.g, Visceral ganglion.
majority live in the sea. .Some, like many Cephalopods and the Pteropods, are pelagic or free-swimming; others creep or lie on the sea bottom.^ In some lizards the scales are small and grainlike, while in others they are large and plate- like.
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^ These two forms are free swimming, are found in the plankton, and do not look much like the adult clam.
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^ A: Cephalopods (including octopi) are different in many ways from all other molluscs.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.Some are littoral, living between tide-marks; others are found at very various depths, up to 2800 fathoms.^ If you find a shell on the beach, be sure to look very carefully though - sometimes another type of animal has found the shell before you, and has taken up residence.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ These crabs did not make the shells that they live in - they simply found empty ones, or in some cases, killed and ate the original gastropod inhabitant.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ The shell characteristics are, for the most part, controlled by genetics, although there can be individual variation within a particular species (some more than others).
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

.A few species have invaded the fresh waters, while the pulmonate and terrestrial Gastropods are distributed over the whole surface of the land in all latitudes and to a height of 15,000 ft.^ There are many different species of conch, and they occur in tropical waters all over the world.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

^ Terrestrial gastropods reduce water loss by sealing the mantle cavity with an extended mantle collar.
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^ Reproductive - Nearly all the members of this class lead an amphibious life, i.e., the larval stage lives in the water and the adult stage lives on the land.
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.As a rule Molluscs are free and more or less active, but many Lamellibranchs are sedentary, and a few of these and of Gastropods are permanently fixed to their habitat.^ Many of these features are directly or indirectly related to their active life and high metabolic rates.
  • OceanLink | Biodviersity - Ask a Marine Scientist 17 January 2010 1:54 UTC oceanlink.island.net [Source type: FILTERED WITH BAYES]

Commensalism occurs in a few instances, but parasitism either external or internal is rare. The latter is confined to certain Gastropods which live in Echinoderms and are extremely degenerate in structure. Protective resemblance is exhibited by some Nudibranch Gastropods which have assumed the colour and appearance of their habitat.
Literature. - I. Morphology. .(i) G. Cuvier, Mimoires pour servir a l'histoire et a l'anatomie des mollusques (Paris, 1816).^ Fk1: Falkner, G.; Ripken, T.E.J.; Falkner, M. 2002: Mollusques Continentaux de France: Liste de Référence Annotée et Bibliographie.

(2) J. Poli, Testacea utriusque Siciliae, eorumque historic et anatome, tabulis aeneis 49 illustrate, vols. i. - iii., fol. (Parma,1791-1795and 1826-1827). .(3) St delle Chiaje, Memorie sulla storia e anatomia degli animali senza vertebre del regno di Napoli (Naples, 1823-1829), new edition with 172 plates, fol., 18 43. (4) J. Vaughan Thompson, Zoological Researches (Cork, 1830); memoir iv., " On the Cirripedes or Barnacles, demonstrating their deceptive character."^ Lampsilis siliquoidea (Barnes, 1823) United States: Michigan: Macomb: Lake St. Clair, New Baltimore approx.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

^ Pyganodon grandis (Say, 1829) United States: New York: : St. Lawrence River, pond on Wellesley Island approx.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

^ Anodonta implicata Say, 1829 Canada: New Brunswick: York: St. John River, at McKinley Ferry, Kingsclear, Kingsclear Parrish approx.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

(5) A. Kowalewsky, " Entwickelungsgeschichte der einfachen Ascidien," in Mtn. de l'acad. des sciences de St Petersbourg (1866), and " Entwickelungsgeschichte des Amphioxus lanceolatus," ibid. (1867). (6) J. Vaughan T hompson,Zoological Researches (Cork,1830); memoir v., "Polyzoa, a new animal discovered as an inhabitant of some Zoophytes." (7) C. G. Ehrenberg, " Die Korallenthiere des Rothen Meeres " (Berlin, 1834); Abhand. d. k. Akad. d. Wissenschaften in Berlin (1832). .(8) H. Milne-Edwards, Recherches sur les polypiers de France (Paris, 184118 44).^ Peringia ulvae (Pennant, 1777) France: Pays de la Loire: Loire-Atlantique: Le Pouliguen approx.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

^ Bithynia muriatica Larmarck France: Pays de la Loire: Loire-Atlantique: Le Pouliguen approx.
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

(9) H. Milne-Edwards, papers in the Annales des sciences naturelles (1841-1860). (to) H. de Lacaze-Duthiers, papers in the Annales des sciences naturelles, e.g. " Anomia " (1854), " Mytilus " (1856), " Dentalium " (1856-1857), " Purpura " (1859), " Haliotis (1859), " Vermetus " (1860). (i I) A. Kolliker, Entwickelungsgeschichte der Cephalopoden (Zurich, 1844). (12) C. G. Gegenbaur, Untersuchungen fiber Pteropoden and Heteropoden, (Leipzig, 1855). .(13) J. W. Spengel, " Die Geruchsorgane and das Nervensystem der Mollusken," Zeitschr.^ Die während der Tagung in Urach im Frühjahr 1967 gesammelten Mollusken.-- Mitt.
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

^ Die während der Tagung in Wien im Mai 1966 gesammelten Mollusken.-- Mitt.
  • science . naturalis - Gittenberger 17 January 2010 1:54 UTC science.naturalis.nl [Source type: Academic]

f. wins. Zool.
(1881). (14) Richard Owen, Memoir on the Pearly Nautilus (London, 1832). (is) L. Cuenot, " Excretion chez les mollusques," Arch. d. biol. xv1. (1899). (16) P. Geddes, " On the Mechanism of the Odontophore in certain Mollusca." (17) T. H. Huxley, " On the Morphology of the Cephalous Mollusca," Phil. Trans. (1853). .(18) Von Jhering, Vergleichende Anatomie des Nervensystems and Phylogenie der Mollusken (Leipzig, 1877).^ Vergleichende Anatomie, Phylogenie und Historische Biogeographie der Ampullariidae.

^ N, 79.1877?W (3) ; Collector: van der Schalie, Henry; 00/Aug/1932; Preparation/Count: Dry 18.0 .
  • UMMZ-Mollusk Division Catalog 21 January 2010 18:018 UTC www.liath.com [Source type: Academic]

(19) E. R. Lankester, " Contributions to the Developmental History of the Mollusca," Phil. Trans. (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart. Journ. Micr. Sci. xxxiv. (1893). (20) P. Pelseneer, Introduction a l'etude des Mollusques (Brussels, 1894); " Recherches sur les Mollusques archaiques," Mem. tour. Acad. belg., 1.VII. (1899); " Mollusca," Lankester's Treatise on Zoology, pt. v. (1906).
I I. Conchology. - (21) Cooke, " Molluscs," Cambridge Natural History, vol. iii. (1895). (22) Fischer, Manuel deconchyliologie (1887). (23) Jeffreys, British Conchology (1862-1869). (24) Simroth, " Mollusca," Bronn's Klassen and Ordnungen des Thierreichs, Bd. iii. (1895), in prog. (25) Tryon, Manual of Conchology (1878), in prog. (26) Woodward, A Manual of the Mollusca (1880). (E. R. L.; J. T. C.)


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

Translingual

Etymology

Proper noun

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Wikipedia has an article on:
Mollusca
  1. a taxonomic phylum, within superphylum Protostomia - the molluscs or mollusks
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Wikispecies has information on:

See also


Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Spiralia
Cladus: Lophotrochozoa
Phylum: Mollusca
Classes: Aplacophora - Polyplacophora - Monoplacophora - Bivalvia - Scaphopoda - Gastropoda - Cephalopoda - †Rostroconchia - †Helcionelloida

References

  • Gordon, D.P. (ed.) .2009: New Zealand inventory of biodiversity.^ In New Zealand inventory of biodiversity.Vol.

    ^ New Zealand inventory of biodiversity.

    ^ New Zealand Biodiversity: 2414 described marine species (Buckeridge & Gordon, 2000 [1] ) etc.

    Volume 1. Kingdom Animalia. .Radiata, Lophotrochozoa, Deuterostomia
    .^ Kingdom Animalia : Radiata, Lophotrochozoa, Deuterostomia .

    Canterbury University Press, Christchurch, New Zealand.
  • McGhie, H.A. 2008: Catalogue of type specimens of molluscs in the collection of The Manchester Museum, The University of Manchester, UK. ZooKeys, 4: 1-46. Abstract PDF

links

Vernacular names

Català: mol·luscs
Corsu: mulluschi
Deutsch: Mollusken, Weichtiere
Ελληνικά: Μαλάκια
English: Molluscs
Español: Moluscos
Français: Mollusques
Galego: Moluscos
한국어: 연체동물
Հայերեն: Փափկամարմիններ
Hrvatski: Mekušci
Italiano: Molluschi
Magyar: Puhatestűek
Македонски: Мекотели
日本語: 軟体動物門
Polski: Mięczaki
Português: Moluscos
Русский: Моллюски
Slovenčina: Mäkkýše
Suomi: Nilviäiset
Svenska: Blötdjur
中文: 软体动物
Wikimedia Commons For more multimedia, look at .Mollusca on Wikimedia Commons.^ Mollusca on Wikimedia Commons .


Simple English

Redirecting to Mollusc


Citable sentences

Up to date as of December 14, 2010

Here are sentences from other pages on Mollusca, which are similar to those in the above article.








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