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See also:MUSSEL (0. Eng. muscle, See also:Lat. musculus, diminutive of See also:mus, See also:mouse, applied to small See also:sea See also:fish and mussels) , a See also:term applied in See also:England to two families of Lamellibranch Molluscs—the marine Mytilacea, of which the edible See also:mussel, Mytilus edulis, is the representative; and the fresh-See also:water Unionidae, of which the See also:river mussel, Unio pictorum, and the See also:swan mussel, Anodonta cygnea, are the See also:common See also: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 See also:account of the frequently very dark See also:colour of their shells . They are somewhat remote from the See also:sea mussels in structure, and have not even a common economic importance . The sea mussel (Mytilus edulis) belongs to the second See also:order of the class See also:Lamellibranchia (q.v.), namely the Filibranchia, distinguished by the comparatively See also:free See also:condition of the gill-filaments, which, whilst adhering to one another to See also:form gill-plates, are yet not fused to one another by concrescence . It is also remarkable for the small See also:size of its See also:foot and the large development of two glands in the foot—the byssus-forming and the byssus-cementing glands . The byssus is a collection ofhorny threads by which the sea mussel (like many other Lamellibranch or bivalve molluscs) fixes itself to stones, rocks or submerged See also:wood, but is not a permanent means of See also:attachment, since it can be discarded by the See also:animal, which, after a certain amount of locomotion, again fixes itself by new secretion of byssus from the foot . Such See also:movement is more frequent in See also:young mussels than in the full-grown . Mytilus possesses no siphonal See also:tube-like productions of the margin of the See also: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 See also:northern See also:Atlantic and in the Mediterranean See also:basin . It presents varieties of form and colour according to the See also:depth of water and other circumstances of its See also:habitat . Usually it is found on the British See also:coast encrusting rocks exposed at See also:low tides, or on the See also:flat surfaces formed by sandbanks overlying See also:clay, the latter See also: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 See also:surface and numbering millions . The readiness with which the young Mytilus attaches itself to wicker-See also:work is made the means of artificially cultivating and securing these molluscs for the See also:market both in the See also:Bay of See also:Kiel in See also:North See also:Germany and at the mouth of the See also:Somme and other spots on the coast of See also:France . Natural scalps are subject to extreme vicissitudes: an See also:area of many acres may be destroyed by a See also:local See also:change of current producing a See also:deposit of See also:sand or See also:shingle over the See also:scalp, or .by exposure to See also:frost at low See also:tide in See also:winter, or by See also:accumulation of decomposing See also:vegetable See also:matter . The See also:chief localities of natural scalps on the British coast are See also:Morecambe Bay in See also:Lancashire and the flat eastern shores, especially that of the See also:Wash of See also:Lincoln, and similar shallow bays . These scalps are in some cases in the hands of private owners, and the See also:Fisheries See also:Department has made arrangements by which some local authorities, e.g . :the See also:corporation of See also:Boston, can See also:lease layings to individuals for the purpose of artificial cultivation . The sea mussel is scarcely inferior in commercial value to the See also:oyster . In 1873 the value of mussels exported from See also:Antwerp alone to See also:Paris to be used as human See also:food was £280,000 . In See also:Britain their chief See also:consumption is in the deep-sea See also:line See also:fishery, where they are held to be the most effective of all baits . Twenty-eight boats engaged in See also:haddock-fishing at See also:Eyemouth used between See also:October 1882 and May 1883 920 tons of mussels (about 47,000,000 individuals), costing nearly £1800 to the fishermen, about one-See also:half of which sum was expended on the See also:carriage of the mussels . The quantity of mussels landed on Scottish coasts has decreased in See also: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 See also:statistics for England and See also:Wales mussels are not separately distinguished . Many See also:thou-sand tons of mussels are wastefully employed as manure by the farmers on lands adjoining scalp-producing coasts, as in Lancashire and See also:Norfolk, three half-pence a See also:bushel being the See also:price quoted in such cases . It is a curious fact, illustrative of the ignorant See also:procedure and arbitrary fashions of See also:fisher-folk, that on the Atlantic seaboard of the See also: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 See also:English or See also:Norwegian fishermen, though abundant on their shores, is employed as bait by the fishermen to the extent of 1i million bushels per annum, valued at £120,000 . At the mouth of the river See also:Conway in North Wales the sea mussel is crushed in large quantities in order to See also:extract pearls of an inferior quality which are occasionally found in these as in other Lamellibranch molluscs (See also:Gwyn See also:Jeffreys) . Mytilus edulis is considered of See also: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 See also:density I014 (the density of the water of the North Sea being 1026) . Experiments made by removing mussels from See also:salt water to brackish, and finally to quite fresh water show that it is even more tolerant of fresh water than the oyster; of See also: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 See also:developed . An account of the See also:anatomy of Anodon is given in the See also:article LAMELLIBRANCHIA . Unio differs in no important point from Anodonta in See also:internal structure . The See also:family Unionidae, to which these genera belong, is of See also:world-wide See also:distribution, and its See also:species occur only in ponds and See also: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 See also:title of "fresh-water mussel." Anodonta cygnea, the See also:Pond Mussel or Swan Mussel, appears to be entirely without economic importance . Unio pictorum, the common river mussel (See also:Thames), appears to owe its name to the fact that the shells were used at one See also:time for holding water-colour paints as now shells of this species and of the sea mussel are used for holding See also:gold and See also:silver paint sold by artists' colourmen, but it has no other economic value . Unio margaritiferus, the See also:pearl mussel, was at one time of considerable importance as a source of pearls, and the pearl mussel fishery is to this See also:day carried on under See also:peculiar See also:state regulations in See also:Sweden and See also:Saxony, and other parts of the See also:continent . In See also:Scotland and See also:Ireland the pearl mussel fishery was also of importance, but has altogether dwindled into insignificance since the 9pening up of commercial intercourse with the See also: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 See also:forty years of the 18th See also:century pearls were exported from the Scotch fisheries to Paris to the value of £too,000; See also:round pearls, the size of a See also:pea, perfect in every respect, were See also:worth £3 or L4 . The pearl mussel was formerly used as bait in the See also:Aberdeen See also:cod fishery . |
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