mus·sel / ˈməsəl/ • n. any of a number of bivalve mollusks with a brown or purplish-black shell, in particular: ∎  a marine bivalve (family Mytilidae) that uses byssus threads to anchor to a firm surface, including the edible mussel (Mytilus edulis). ∎  a freshwater bivalve (family Unionidae) that typically lies on the bed of a river, some species forming small pearls.

mussel Any of several species of bivalve molluscs with thin, oval shells. Marine species of the family Mytilidae are found throughout the world in colonies on sea walls and rocky shores, where they attach themselves by means of strands called byssus threads. The edible mussel, Mytilus edulis, is sometimes cultivated on ropes hanging from rafts. Freshwater mussels of the family Unionidae, found in n continents only, produce pearls.

mussel bivalve mollusc. OE. mus(c)le, muxle (— L.), and — MLG. mussel, MDu. mosscele (Du. mossel) — Rom. *muscula, alt. f. L. musculus, dim. (see -CLE) of L. mūs MOUSE.