A class of mollusks characterized by having two hinged shells that can open and close, including clams, oysters, mussels, and scallops. Most are filter feeders that live in aquatic environments.
From Latin 'bi' meaning two and 'valva' meaning leaf of a folding door, literally 'two-valved.' The name describes the characteristic two-part shell that opens and closes like a hinged door, established when early taxonomists classified mollusks by shell structure.
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