mussel edible freshwater or marine bivalve mollusk. Mussels are able to move slowly by means of the muscular foot. They feed and breathe by filtering water through extensible tubes called siphons; a large mussel filters 10 gal (38 liters) of water per day. The close-fitting shells protect the mussel from desiccation and enable it to live high up on the shore. Most marine mussels belong to the single family, Mytilidae. They are widespread and are especially abundant in cooler seas. They form extensive, crowded beds, anchoring themselves by the byssus, a secretion of strong threads. The blue mussel grows up to 3 in. (7.6 cm) and is common along the Atlantic coast; the smaller hooked mussel has a more southerly range. The horse mussel, found in deeper waters, grows to 6 in. (15 cm) in length. Freshwater mussels are chiefly of two kinds: the large, dark-shelled burrowing mussels, a source of pearls and of mother-of-pearl; and the tiny "fingernail clams" found on the bottoms of clear pools and brooks. The zebra mussel, Dreissen polymorpha, is a small freshwater mussel native to Europe that was introduced in the 1980s into the Great Lakes. Lacking natural predators, it has proliferated and spread, clogging intake pipes at water and power facilities and disrupting native ecosystems. The quagga mussel, Dreissena rostriformis bugensis, also native to Europe, was first found in the Great Lakes in 1989 and has largely supplanted the zebra mussel there. Quagga populations are also found in the Colorado River basin and in aqueducts, canals, and reservoirs connected to the river. Freshwater mussels (family Unionidae), sometimes called clams , pass through a parasitic larval state, living on the fins, gills, and bodies of fishes. The familiar jingle shells, delicate, shiny orange or yellow shells common on beaches, belong to the same order as the marine mussel. Mussels are classified in the phylum Mollusca , class Pelecypoda or Bivalvia, order Filibranchia.
