Mussel, a name applied to several common bivalves or Lamellibranch molluscs. (1) The Common Sea-mussel (Mytilus edulis), very important for bait and not unfrequently used as food, is widely distributed in crowded 'beds' between high and low water marks. It is usually sedentary, and firmly anchored by yellowish silken 'byssus,' but it is also able to shift its quarters and even to climb by slowly extending the range of the byssal thread exuded from the 'foot.' (2) The Horse-mussel (Modiolus modiola) is nearly twice as large as the above, and lives a more active burrowing life below the low-water mark. It is never used for food, and is not available for bait. Both these sea-mussels are representative of large genera, and are included in one family—Mytilidae. (3) Quite different from the above are the fresh-water mussels, Unionidae, widely distributed in lakes and rivers, where they plough their way slowly along the bottom from one resting-place to another. As good representatives of the Unionidae, the Pond-mussel, Anodon cygnea, the Painter's Mussel, Unio pictorum, whose shells were once used for holding water-colour paints, and the Pearl-mussel, Margaritana margaritifera (see PEARL), may be noted. For the structure and general characters, see BIVALVES.
The common edible mussel abounds on the Atlantic seaboard of the United States, but is used neither as food nor as bait. In England it is largely used as human food; in Scotland it is not so used, but enormous quantities are required for bait, especially by haddock fishers. The chief objection to mussels as food is that they are occasionally poisonous. Mussels especially which are unhealthy or dead are very apt to contain dangerously poisonous waste-products; care should accordingly be taken that those used for food are thoroughly fresh. A French Commission reported in 1889 that the poison is due to the presence in the mussel of a volatile alkaloid developed under the influence of a particular microbe, which is only found in mussels growing in stagnant and polluted water. Sewage fairly free from the pollution of manufactories is distinctly beneficial to mussel culture. It is said on good authority that mussels lose any poisonous properties they may have if cooked for ten minutes with carbonate of soda. The wasteful and unregulated consumption of mussels from the scalps on the British coasts, the reckless destruction of immature mussels, and the wholly inadequate efforts at artificial mussel culture have caused in some parts of Britain a mussel famine, and necessitated large importations from abroad. Great natural scalps on the British coasts are those of the Wash, Morecambe Bay, and the estuary of the Clyde. The last, from which it is computed that since 1840 one hundred thousand tons of mussels have been taken, is now exhausted and unproductive. The cultivation is practised in the Thames estuary and the Medway, in the Teign and Exe, at Montrose, and elsewhere; but large supplies are imported from Holland. Scotland imports from England, the north of Ireland, and Hamburg. In one year the Eyemouth fishermen have used nine hundred and twenty tons of mussels, mainly imported, and costing £1800. Yet in Lancashire and Norfolk mussels are wastefully used as manure. Mussels may be cultivated either on natural beds—especially where clean gravelly bottoms are exposed at low-water, and where salt and fresh water mix—by transplanting spat and protecting young mussels; or in deep water, where transplantation may also be practised. In north Germany and north France mussels are successfully cultivated on wicker-work attached to palisades. The Dutch artificial beds are mainly provided with spat from the coasts of Essex and Kent.