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Mussel
Blue mussels Mytilus edulis in the intertidal zone in Cornwall, England
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclasses

Pteriomorpha (marine mussels)
Palaeoheterodonta (freshwater mussels)
Heterodonta (zebra mussels)

The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.

The word "mussel" is most frequently used to mean the edible bivalves of the marine family Mytilidae, most of which live on exposed shores in the intertidal zone, attached by means of their strong byssal threads ("beard") to a firm substrate. A few species (in the genus Bathymodiolus) have colonized hydrothermal vents associated with deep ocean ridges.

In most marine mussels the shell is longer than it is wide, being wedge-shaped or asymmetrical. The external color of the shell is often dark blue, blackish, or brown, while the interior is silvery and somewhat nacreous.

A bed of blue mussels, Mytilus edulis, in the intertidal zone in northern Norway

The word "mussel" is also used for many freshwater bivalves, including the freshwater pearl mussels. Freshwater mussel species inhabit lakes, ponds, rivers, creeks, canals, and similar habitats. These bivalves belong to several allied families, the largest family being the Unionidae. They are not closely related to saltwater mussels; they are taxonomically grouped in a different subclass, despite some very superficial similarities in appearance.

Freshwater Zebra mussels and their relatives in the family Dreissenidae are not related to previously mentioned groups, even though they resemble many Mytilus species in shape, and live attached to rocks and other hard surfaces in a similar manner, using a byssus. They are classified with the Heterodonta, the taxonomic group which includes most of the bivalves commonly referred to as "clams".

A freshwater mussel from the Netherlands, Unio pictorum (from the family Unionidae), commonly known as the "Painter's mussel". Individual shell valves of this species were used by painters as a small dish in which to mix pigments.

Contents

General anatomy

Marine blue mussel, Mytilus edulis, showing some of the inner anatomy. The white posterior adductor muscle is visible in the upper image, and has been cut in the lower image to allow the valves to open fully

The mussel's external shell is composed of two hinged halves or "valves". The valves are joined together on the outside by a ligament, and are closed when necessary by strong internal muscles. Mussel shells carry out a variety of functions, including support for soft tissues, protection from predators and protection against desiccation.

The shell is made of three layers. In the pearly mussels there is an inner iridescent layer of nacre (mother-of-pearl) composed of calcium carbonate, which is continuously secreted by the mantle; the prismatic layer, a middle layer of chalky white crystals of calcium carbonate in a protein matrix; and the periostracum, an outer pigmented layer resembling a skin. The periostracum is composed of a protein called conchin, and its function is to protect the prismatic layer from abrasion and dissolution by acids (especially important in freshwater forms where the decay of leaf materials produces acids).

Like most bivalves, mussels have a large organ called a foot. In freshwater mussels, the foot is large, muscular, and generally hatchet-shaped. It is used to pull the animal through the substrate (typically sand, gravel, or silt) in which it lies partially buried. It does this by repeatedly advancing the foot through the substrate, expanding the end so it serves as an anchor, and then pulling the rest of the animal with its shell forward. It also serves as a fleshy anchor when the animal is stationary.

A Mytilus with its byssus clearly showing, at Ocean Beach, San Francisco, California

In marine mussels, the foot is smaller, tongue-like in shape, with a groove on the ventral surface which is continuous with the byssus pit. In this pit, a viscous secretion is exuded, entering the groove and hardening gradually upon contact with sea water. This forms extremely tough, strong, elastic, byssus threads that secure the mussel to its substrate. The byssus thread is also sometimes used by mussels as a defensive measure, to tether predatory molluscs, such as dog whelks, that invade mussel beds, immobilising them and thus starving them to death.

In cooking, the byssus of the mussel is known as the "beard" and is removed before the mussels are prepared.

Life habits

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Feeding

Both marine and freshwater mussels are filter feeders; they feed on plankton and other microscopic sea creatures which are free-floating in seawater. A mussel draws water in through its incurrent siphon. The water is then brought into the branchial chamber by the actions of the cilia located on the gills for cilliary-mucus feeding. The wastewater exits through the excurrent siphon. The labial palps finally funnel the food into the mouth, where digestion begins.

Marine mussels are usually found clumping together on wave-washed rocks, each attached to the rock by its byssus. The clumping habit helps hold the mussels firm against the force of the waves. At low tide mussels in the middle of a clump will undergo less water loss because of water capture by the other mussels.

Mussel output in 2005

Reproduction

Both marine and freshwater mussels are gonochoristic, with separate male and female individuals. In marine mussels, fertilization occurs outside the body, with a larval stage that drifts for three weeks to six months, before settling on a hard surface as a young mussel. There, it is capable of moving slowly by means of attaching and detaching byssal threads to attain a better life position.

Freshwater mussels also reproduce sexually. Sperm released by the male directly into the water enters the female via the incurrent siphon. After fertilization, the eggs develop into a larval stage called a glochidium (plural glochidia), which temporarily parasitize fish, attaching themselves to the fish's fins or gills. Prior to their release, the glochidia grow in the gills of the female mussel where they are constantly flushed with oxygen-rich water. In some species, release occurs when a fish attempts to attack the mussel's minnow or other prey species-shaped mantle flaps, an example of aggressive mimicry.

Glochidia are generally species-specific, and will only live if they find the correct fish host. Once the larval mussels attach to the fish, the fish body reacts to cover them with cells forming a cyst, where the glochidia remain for two to five weeks (depending on temperature). They grow, break free from the host, and drop to the bottom of the water to begin an independent life.

Predators

A starfish consuming a mussel in Northern California

Marine mussels are eaten by humans, sea stars, seabirds, and by numerous species of predatory marine gastropods in the family Muricidae, such as the dog whelk, Nucella lapillus.

Freshwater mussels are eaten by otters, raccoons, ducks, and geese.

Distribution and habitat

A stamp from the Faroe Islands showing Modiolus modiolus, the horse mussel

Marine mussels are abundant in the low and mid intertidal zone in temperate seas globally.

Other species of marine mussel live in tropical intertidal areas, but not in the same huge numbers as in temperate zones.

Certain species of marine mussels prefer salt marshes or quiet bays, while others thrive in pounding surf, completely covering wave-washed rocks. Some species have colonized abyssal depths near hydrothermal vents. The South African white mussel exceptionally doesn't bind itself to rocks but burrows into sandy beaches extending two tubes above the sand surface for ingestion of food and water and exhausting wastes

Freshwater mussels inhabit permanent lakes, rivers, canals and streams throughout the world except in the polar regions. They require a constant source of cool, clean water. They prefer water with a substantial mineral content, using calcium carbonate to build their shells.

Aquaculture

Bouchots are marine pilings for growing mussels, here shown at an agricultural fair

In 2005, China accounted for 40 per cent of the global mussel catch according to a FAO study.[1] Within Europe, Spain remained the industry leader. In North America, 80% of cultured mussels are produced in Prince Edward Island in Canada.[2]

Freshwater mussels are used as host animals for the cultivation of freshwater pearls. Some species of marine mussel, including the Blue Mussel (Mytilus edulis) and the New Zealand green-lipped mussel (Perna canaliculus), are also cultivated as a source of food.

There are a variety of techniques for growing mussels.

  • Intertidal growth technique, or bouchot technique: pilings, known in French as bouchots, are planted at sea; ropes, on which the mussels grow, are tied in a spiral on the pilings; some mesh netting prevents the mussels from falling away. This method needs an extended tidal zone.
  • Mussels are cultivated extensively in New Zealand, where the most common method is to attach mussels to ropes which are hung from a rope back-bone supported by large plastic floats. The most common species cultivated in New Zealand is the New Zealand green-lipped mussel.

Mussels as food

Mussels at Trouville fish market
The flesh of cooked mussels can be orange, or pale yellow.

Humans have used mussels as food for thousands of years and continue to do so. In Belgium, the Netherlands, and France, mussels (called moules marinières) are consumed with french fries ("mosselen met friet" or "moules frites") or bread. In France, the Éclade des Moules is a mussel bake popular along the beaches of the Bay of Biscay. In Italy, often mixed with other sea food, or eaten with pasta. In Turkey, mussels are either covered with flour and fried on shishs ('midye tava'), or filled with rice and served cold ('midye dolma') and are usually consumed with alcohol (mostly with raki or beer). In Cantonese cuisine, mussels are cooked in a broth of garlic and fermented black bean. In New Zealand, they are served in a chili-based vinaigrette.

During the second World War in the United States, mussels were commonly served in diners. This was due to the unavailability of red meat related to wartime rationing.[3] They are used in Ireland boiled and seasoned with vinegar, with the "bray" or boiling water as a supplementary hot drink.

In India mussels are popular in Kerala, Bhatkal, and Goa. They are either prepared with drumsticks, breadfruit or other vegetables, or filled with rice and coconut paste with spices and served hot. Fried mussels of north Kerala are a spicy, favored delicacy.

Mussels can be smoked, boiled, steamed or fried in batter.

As with all shellfish, mussels should be checked to ensure they are still alive just before they are cooked; they quickly become toxic after dying.[citation needed] A simple criterion is that live mussels, when in the air, will shut tightly when disturbed. Open, unresponsive mussels are dead, and must be discarded. Unusually heavy, wild caught, closed mussels may be discarded as they may contain only mud or sand. (They can be tested by slightly opening the shell halves.)

A thorough rinse in water and removal of "the beard" is suggested. Mussel shells open when cooked, revealing the cooked soft parts.

Commercial mussel fishermen unloading a cargo of mussels in Donegal, Ireland.

In Belgium, mussels are often served with fresh herbs and flavorful vegetables in a stock of butter and white wine. Frites/Frieten and Belgian beer are popular accompaniments. Months ending in "-ber" (September to December) are said to be the "in" season for mussels.

In the Netherlands, mussels are sometimes served fried in batter or breadcrumbs, particularly at take-out food outlets or informal settings.

Although mussels are valued as food, mussel poisoning due to toxic planktonic organisms can be a danger along some coastlines. For instance, mussels should be avoided along the west coast of the United States during the warmer months. This poisoning is usually due to a bloom of dinoflagellates (red tides), which contain toxins. The dinoflagellates and their toxin are harmless to mussels, even when concentrated by the mussel's filter feeding, but if the mussels are consumed by humans, the concentrated toxins cause serious illness, such as paralytic shellfish poisoning. Usually the U.S. government monitors the levels of toxins throughout the year at fishing sites. See Red Tide.

Freshwater mussels nowadays are generally considered to be unpalatable, though the native peoples in North America utilized them extensively.

Nutrition highlights

Raw blue mussels[4]
Serving size 3 ounces
Calories 73
Protein 10.1 g
Carbohydrate 3.1 g
Fiber 0.0 g
Total fat 1.9 g
Saturated fat 0.4 g
Sodium 243 mg

Foods that are an “excellent source” of a particular nutrient provide 20% or more of the recommended daily value. Foods that are a “good source” of a particular nutrient provide between 10 and 20% of the recommended daily value.

See also

References

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

MUSSEL (0. Eng. muscle, Lat. musculus, diminutive of mus, mouse, applied to small sea fish and mussels), a term applied in England to two families of Lamellibranch Molluscs - the marine Mytilacea, of which the edible mussel, Mytilus edulis, is the representative; and the fresh-water Unionidae, of which the river mussel, Unio pictorum, and the swan mussel, Anodonta cygnea, are the common British examples. It is not obvious why these fresh-water forms have been associated popularly with the Mytilacea under the name mussel, unless it be on account of the frequently very dark colour of their shells. They are somewhat remote from the sea mussels in structure, and have not even a common economic importance.

The sea mussel (Mytilus edulis) belongs to the second order of the class Lamellibranchia, namely the Filibranchia, distinguished by the comparatively free condition of the gillfilaments, which, whilst adhering to one another to form gillplates, are yet not fused to one another by concrescence. It is also remarkable for the small size of its foot and the large development of two glands in the foot - the byssus-forming and the byssus-cementing glands. The byssus is a collection of horny threads by which the sea mussel (like many other Lamellibranch or bivalve molluscs) fixes itself to stones, rocks or submerged wood, but is not a permanent means of attachment, since it can be discarded by the animal, which, after a certain amount of locomotion, again fixes itself by new secretion of byssus from the foot. Such movement is more frequent in young mussels than in the full-grown. Mytilus possesses no siphonal tube-like productions of the margin of the mantle-skirt, nor any notching of the same, representative of the siphons which are found in its fresh-water ally, the Dreissensia polymorpha. Mytilus edulis is an exceedingly abundant and widely distributed form. It occurs on both sides of the northern Atlantic and in the Mediterranean basin. It presents varieties of form and colour according to the depth of water and other circumstances of its habitat. Usually it is found on the British coast encrusting rocks exposed at low tides, or on the flat surfaces formed by sandbanks overlying clay, the latter kind of colonies being known locally as "scalps." Under these conditions it forms continuous masses of individuals closely packed together, sometimes extending over many acres of surface and numbering millions. The readiness with which the young Mytilus attaches itself to wicker-work is made the means of artificially cultivating and securing these molluscs for the market both in the Bay of Kiel in North Germany and at the mouth of the Somme and other spots on the coast of France.

Natural scalps are subject to extreme vicissitudes: an area of many acres may be destroyed by a local change of current producing a deposit of sand or shingle over the scalp, or by exposure to frost at low tide in winter, or by accumulation of decomposing vegetable matter. The chief localities of natural scalps on the British coast are Morecambe Bay in Lancashire and the flat eastern shores, especially that of the Wash of Lincoln, and similar shallow bays. These scalps are in some cases in the hands of private owners, and the Fisheries Department has made arrangements by which some local authorities, e.g. the corporation of Boston, can lease layings to individuals for the purpose of artificial cultivation.

The sea mussel is scarcely inferior in commercial value to the oyster. In 1873 the value of mussels exported from Antwerp alone to Paris to be used as human food was £280,000. In Britain their chief consumption is in the deep-sea line fishery, where they are held to be the most effective of all baits. Twenty-eight boats engaged in haddock-fishing at Eyemouth used between October 1882 and May 1883 920 tons of mussels (about 47,000,000 individuals), costing nearly £1800 to the fishermen, about one-half of which sum was expended on the carriage of the mussels. The quantity of mussels landed on Scottish coasts has decreased in recent years owing to the decline in the line fisheries. In 1896 the quantity was over 243,000 cwts., valued at £14,950; in 1902 it was only 95,663 cwts., valued at £5976.. In the statistics for England and Wales mussels are not separately distinguished. Many thousand tons of mussels are wastefully employed as manure by the farmers on lands adjoining scalp-producing coasts, as in Lancashire and Norfolk, three half-pence a bushel being the price quoted in such cases. It is a curious fact, illustrative of the ignorant procedure and arbitrary fashions of fisher-folk, that on the Atlantic seaboard of the United States the sea mussel, Mytilus edulis, though common, is not used as bait nor as food. Instead, the soft clam, Mya arenaria, a Lamellibranch not used by English or Norwegian fishermen, though abundant on their shores, is employed as bait by the fishermen to the extent of 14 million bushels per annum, valued at £120,000. At the mouth of the river Conway in North Wales the sea mussel is crushed in large quantities in order to extract pearls of an inferior quality which are occasionally found in these as in other Lamellibranch molluscs (Gwyn Jeffreys).

Mytilus edulis is considered of fair size for eating when it is 2 in. in length, which size is attained in three years after the spat or young mussel has fixed itself. Under favourable circumstances it will grow much larger than this, specimens being recorded of 9 in. in length. It is very tolerant of fresh water, fattening best, as does the oyster, in water of density 1014 (the density of the water of the North Sea being 1026). Experiments made by removing mussels from salt water to brackish, and finally to quite fresh water show that it is even more tolerant of fresh water than the oyster; of thirty mussels so transferred all were alive after fifteen days. Mytilus edulis is occasionally poisonous, owing to conditions not satisfactorily determined.

The fresh-water Mussels, Anodonta cygnea, Unio pictorum, and Unio margaritiferus belong to the order Eulamellibranchia of Lamellibranch Molluscs, in which the anterior and posterior adductor muscles are equally developed. An account of the anatomy of Anodon is given in the article Lamellibranchia. Unio differs in no important point from Anodonta in internal structure. The family Unionidae, to which these genera belong, is of world-wide distribution, and its species occur only in ponds and rivers. A vast number of species arranged in several genera and sub-genera have been distinguished, but in the British Islands the three species above named are the only claimants to the title of "fresh-water mussel." Anodonta cygnea, the Pond Mussel or Swan Mussel, appears to be entirely without economic importance. Unio pictorum, the common river mussel (Thames), appears to owe its name to the fact that the shells were used at one time for holding water-colour paints as now shells of this species and of the sea mussel are used for holding gold and silver paint sold by artists' colourmen, but it has no other economic value. Unio margaritiferus, the pearl mussel, was at one time of considerable importance as a source of pearls, and the pearl mussel fishery is to this day carried on under peculiar state regulations in Sweden and Saxony, and other parts of the continent. In Scotland and Ireland the pearl mussel fishery was also of importance, but has altogether dwindled into insignificance since the opening up of commercial intercourse with the East and with the islands of the Pacific Ocean, whence finer and more abundant pearls than those of Unio margaritiferus are derived.

In the last forty years of the 18th century pearls were exported from the Scotch fisheries to Paris to the value of £Ioo,000; round pearls, the size of a pea, perfect in every respect, were worth £3 or £4. The pearl mussel was formerly used as bait in the Aberdeen cod fishery.

LITERATURE. - For an account of the anatomy of Mytilus edulis the reader is referred to the treatise by Sabatier on that subject (Paris, 1875). The essay by Charles Harding on Molluscs used for Food or Bait, published by the committee of the London International Fisheries Exhibition (1883), may be consulted as to the economic questions connected with the sea mussel. The development of this species is described by Wilson in Fifth Ann. Rep. Scot. Fish. Board (1887). (E. R. L.; J. T. C.)


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Simple English

Mussel
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclasses

Pteriomorpha (marine mussels)
Palaeoheterodonta (freshwater mussels)
Heterodonta (zebra mussels)

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Mussels are several families of bivalve molluscs. Mussels live in lakes, rivers, and creeks. The sometimes also live in intertidal areas along coastlines worldwide. The freshwater mussels (several allied families, the largest being the Unionidae) and saltwater mussels (family Mytilidae) are not closely related, despite the fact that they may look similar. They are grouped in different subclasses. The freshwater Zebra mussels and their relatives (family Dreissenidae) live attached to rocks in a manner similar to marine mussels, but are classified with the Heterodonta, the taxonomic group including most bivalves referred to as "clams".

From archeology, it is known that humans have been eating mussels for thousands of years. They can be cooked or eaten raw. Care must be taken however as mussels quickly become poisonous after they die.

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