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Squid
Fossil range: (at least) Late Cretaceous–Recent[1]
Bigfin Reef Squid, Sepioteuthis lessoniana
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Coleoidea
Superorder: Decapodiformes
Order: Teuthida
A. Naef, 1916
Suborders

Plesioteuthididae (incertae sedis)
Myopsina
Oegopsina

Squid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two longer tentacles. (The only known exception is the bigfin squid group, which have ten very long, thin arms of equal length.)

Contents

Modification from ancestral forms

Squid have differentiated from their ancestral molluscs in such a way that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. What before may have been the foot of the ancestor is now modified into a complex set of tentacles and highly developed sense organs, including advanced eyes similar to those of vertebrates.

The ancestral shell has been lost, with only an internal gladius, or pen, remaining. The pen is a feather-shaped internal structure which supports the squid's mantle and serves as a site for muscle attachment. It is made of a chitin-like substance.

Anatomy

Photo of squid with 8 short arms and two longer tentacles
European Squid (Loligo vulgaris)

The main body mass is enclosed in the mantle, which has a swimming fin along each side. These fins, unlike in other marine organisms, are not the main source of locomotion in most species.

The skin is covered in chromatophores, which enable the squid to change color to suit its surroundings, making it effectively invisible. The underside is also almost always lighter than the topside, to provide camouflage from both prey and predator.

Under the body are openings to the mantle cavity, which contains the gills (ctenidia) and openings to the excretory and reproductive systems. At the front of the mantle cavity lies the siphon, which the squid uses for locomotion via precise jet propulsion. In this form of locomotion, water is sucked into the mantle cavity and expelled out of the siphon in a fast, strong jet. The direction of the siphon can be changed, to suit the direction of travel.

Inside the mantle cavity, beyond the siphon, lies the visceral mass, which is covered by a thin, membranous epidermis. Under this are all the major internal organs.

Nervous system

The giant axon, which may be up to 1 mm (.04 inches) in diameter in some larger species, innervates the mantle and controls part of the jet propulsion system.

As a cephalopod, squid exhibit relatively high intelligence among invertebrates. For example, groups of Humboldt squid hunt cooperatively, using active communication. (See Cephalopod intelligence.)

Reproductive system

Photo of dozens of objects shaped like baby carrots arranged radially in several layers
Egg cases laid by the female squid

In females the ink sac is hidden from view by a pair of white nidamental glands, which lie anterior to the gills. There are also red-spotted accessory nidamental glands. Both organs are associated with food manufacture and shells for the eggs. Females also have a large translucent ovary, situated towards the posterior of the visceral mass.

Males do not possess these organs, but instead have a large testis in place of the ovary, and a spermatophoric gland and sac. In mature males, this sac may contain spermatophores, which are placed inside the female's mantle during mating.

Digestive system

Like all cephalopods, squid have complex digestive systems. The muscular stomach is found roughly in the midpoint of the visceral mass. From there, the bolus moves into the caecum for digestion. The caecum, a long, white organ, is found next to the ovary or testis. In mature squid, more priority is given to reproduction such that the stomach and caecum often shrivel up during the later life stages. Finally, food goes to the liver (or digestive gland), found at the siphon end, for absorption. Solid waste is passed out of the rectum. Beside the rectum is the ink sac, which allows a squid to rapidly discharge black ink into the mantle cavity.

Diagram labeling siphon, intestine, nidamental gland, accessory nidamental gland, renal pore, and branchial heart.
Ventral view of the viscera of the female Chtenopteryx sicula

Cardiovascular system

Squid have three hearts. Two brachial hearts feed the gills, each surrounding the larger systemic heart that pumps blood around the body. The faintly greenish hearts are surrounded by the renal sacs - the main excretory system. The kidneys are difficult to identify and stretch from the hearts (located at the posterior side of the ink sac) to the liver. The systemic heart is made of three chambers, a lower ventricle and two upper auricles.

Head

The head end bears 8 arms and 2 tentacles (species in the bigfin squid group have 10 identical arms), each a form of muscular hydrostat containing many suckers along the edge. These tentacles do not grow back if severed. In the mature male, one basal half of the left ventral tentacle is hectocotylised — and ends in a copulatory pad rather than suckers. It is used for intercourse.

The mouth is equipped with a sharp horny beak mainly made of chitin[2] and cross-linked proteins, and is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain minerals, unlike the teeth and jaws of many other organisms, including marine species.[3] Captured whales often have indigestible squid beaks in their stomachs. The mouth contains the radula (the rough tongue common to all molluscs except bivalvia and aplacophora).

The eyes, on either side of the head, each contain a hard lens. The lens is focused through movement, much like the lens of a camera or telescope, rather than changing shape as the lens in the human eye does.

Size

The majority are no more than 60 centimetres (24 in) long, although the giant squid may reach 13 metres (43 ft).[4]

In 1978, sharp, curved claws on the suction cups of squid tentacles cut up the rubber coating on the hull of the USS Stein. The size suggested the largest squid known at the time.[5]

In 2003, a large specimen of an abundant[6] but poorly understood species, Mesonychoteuthis hamiltoni (the Colossal Squid), was discovered. This species may grow to 14 metres (46 ft) in length, making it the largest invertebrate.[7] Squid have the largest eyes in the animal kingdom. Giant squid are featured in literature and folklore with a frightening connotation. The Kraken is a legendary tentacled monster possibly based on sightings of real giant squid.

In February 2007, a New Zealand fishing vessel caught a Colossal Squid weighing 495 kilograms (1,090 lb) and measuring around 10 metres (33 ft) off the coast of Antarctica.[8]

Classification

Squid are members of the class Cephalopoda, subclass Coleoidea, order Teuthida, of which there are two major suborders, Myopsina and Oegopsina (including giant squids like Architeuthis dux). Teuthida is the largest cephalopod order with around 300 classified into 29 families.

The order Teuthida is a member of the superorder Decapodiformes (from the Greek for "ten legs"). Two other orders of decapodiform cephalopods are also called squid, although they are taxonomically distinct from Teuthida and differ recognizably in their gross anatomical features. They are the bobtail squid of order Sepiolida and the ram's horn squid of the monotypic order Spirulida. The vampire squid, however, is more closely related to the octopuses than to any squid.

Commercial fishing

According to the FAO, the cephalopod catch for 2002 was 3,173,272 tonnes (6.995867×109 lb). Of this, 2,189,206 tonnes, or 75.8 percent, was squid.[9] The following table lists the squid species fishery catches which exceeded 10,000 tonnes (22,000,000 lb) in 2002.

World squid catch in 2002[9]
Species Family Common name Catch
tonnes
Percent
Loligo gahi Loliginidae Patagonian squid 24,976 1.1
Loligo pealei Loliginidae Longfin squid 16,684 0.8
Common squids nei[10] Loliginidae 225,958 10.3
Ommastrephes bartrami Ommastrephidae Neon flying squid 22,483 1.0
Illex argentinus Ommastrephidae Argentine shortfin squid 511,087 23.3
Dosidicus gigas Ommastrephidae Jumbo flying squid 406,356 18.6
Todarodes pacificus Ommastrephidae Japanese flying squid 504,438 23.0
Nototoda russloani Ommastrephidae Wellington flying squid 62,234 2.8
Squids nei[10] Various 414,990 18.6
Total squid 2,189,206 100.0

As food

Photo of rings of breaded, fried squid
Fried calamari: breaded, deep-fried squid

Many species are popular as food in cuisines as diverse as Greek, Turkish, Japanese, Italian, Spanish ,Korean and Indian.

In English-speaking countries, squid as food is often marketed using the Italian word calamari.

Squid are found abundantly in certain areas, and provide large catches for fisheries.

The body can be stuffed whole, cut into flat pieces or sliced into rings. The arms, tentacles and ink are also edible; in fact, the only parts that are not eaten are the beak and gladius (pen).

Squid is a food high in Selenium, Vitamin B12, and Riboflavin.[11]

See also


References

  1. ^ Tanabe, K.; Hikida, Y.; Iba, Y. (2006), "Two Coleoid Jaws from the Upper Cretaceous of Hokkaido, Japan", Journal of Paleontology 80 (1): 138–145, doi:10.1666/0022-3360(2006)080[0138:TCJFTU2.0.CO;2] 
  2. ^ Clarke, M.R. (1986). A Handbook for the Identification of Cephalopod Beaks. Oxford: Clarendon Press. ISBN 0-19-857603-X. 
  3. ^ Miserez, A; Li, Y; Waite, H; Zok, F (2007). "Jumbo squid beaks: Inspiration for design of robust organic composites". Acta Biomaterialia 3: 139–149. doi:10.1016/j.actbio.2006.09.004. 
  4. ^ O'Shea, S. (2003.). "Giant Squid and Colossal Squid Fact Sheet". The Octopus News Magazine Online.. http://www.tonmo.com/science/public/giantsquidfacts.php. 
  5. ^ Johnson, C. Scott "Sea Creatures and the Problem of Equipment Damage" United States Naval Institute Proceedings August 1978 pp.106-107
  6. ^ Xavier, J.C., P.G. Rodhouse, P.N. Trathan & A.G. Wood 1999. A Geographical Information System (GIS) Atlas of cephalopod distribution in the Southern Ocean.PDF Antarctic Science 11:61-62. online version
  7. ^ Anderton, H.J. (2007.). "Amazing specimen of world's largest squid in NZ". New Zealand Government website. http://www.beehive.govt.nz/ViewDocument.aspx?DocumentID=28451. 
  8. ^ "Microwave plan for colossal squid". BBC News. March 22, 2007. http://news.bbc.co.uk/2/hi/asia-pacific/6478801.stm. 
  9. ^ a b Rodhouse, Paul G (2005). "Review of the state of world marine fishery resources: Fisheries technical paper". World squid resources (FAO) (447). ISBN 95-5-105267-0. http://www.fao.org/docrep/009/y5852e/Y5852E08.htm#ch3.2. 
  10. ^ a b nei: not elsewhere included
  11. ^ http://www.nmfs.noaa.gov/fishwatch/species/market_squid.htm

External links


Simple English

Squid
File:Sepioteuthis lessoniana (Bigfin reef squid).jpg
Bigfin Reef Squid, Sepioteuthis lessoniana
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Coleoidea
Superorder: Decapodiformes
Order: Teuthida
A. Naef, 1916
Suborders

†Plesioteuthididae (incertae sedis)
Myopsina
Oegopsina

The squid is an invertebrate animal that lives in the ocean. Squid are hunted by some whales, most notably the Orca (Killer) Whale. Squid, like cuttlefish, have eight arms and two tentacles arranged in pairs.

Characteristics

Reef Squid]]

Squids have several species, but they have some common characteristics. For instance, all squids have tentacles with suckers, a mouth with a radula, and jet propulsion with the siphon from the mantle. The radulla is a scraping organ in the mouth that scrapes nutrients from food sources. Tentacles are long extensions of specialized tissues from the body that are used for locomotive power and capturing food sources. All squids are carnivores; they eat other animals, not plants.

Family

Squids belong to Phylum Mollusca, Class Cephalopoda, which is considered to contain some of the most intelligent invertebrate species. Squids have a cephalized structure, which concentrates sensory organs and complex brains into the anterior end, also known as the head. Although the squids and other cephalopods lack exterior shells and other characteristics of mollusks, they have vestiges of the shell.

Squid Reproduction

After a male and female mate, the female squid lays eggs. The eggs are laid inside an egg case, and since the squid is usually a part of a shoal, it is laid with many other egg cases from many other mother squids, and then anchored to the sea floor. Because of this, squid eggs are often (many times) found in clumps, and those clumps often look like a flower.

Often, the male will die a short time after mating, and the female will die once she has released her eggs. Because of this, squids usually lay eggs only once. Squids do not live very long. Although there are some long-lived species, most squids live for only one or two years.

Look up Teuthida in Wikispecies, a directory of species








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