aquatic mollusk of the class Pelecypoda ("hatchet-foot") or Bivalvia, with a laterally compressed body and a shell consisting of two valves, or movable pieces, hinged by an elastic ligament. Bivalves, which include clams, cockles, mussels, oysters, and scallops, are an important food source for humans, as well as for gastropods, fish, and shore birds.
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