Any mollusc belonging to the taxonomic class Bivalvia, characterized by a shell consisting of two hinged sections, such as a scallop, clam, mussel or oyster.
A pericarp in which the seed case opens or splits into two parts or valves.
Any of certain other bivalves of somewhat similar appearance, such as the zebra mussel and quagga mussel of the family Dreissenidae in subclass Heterodonta.
A saltwater mussel, usually edible, of the order Mytilida in subclass Pteriomorphia.
A freshwater mussel, usually edible, of the order Unionida in subclass Palaeoheterodonta.