plural noun

Definition of Unionidae

: a very large family of freshwater mussels (suborder Submytilacea) having a pearly often roughly sculptured shell with a thick epidermis and larvae that pass through a glochidium stage and being represented in nearly all parts of the world but chiefly in North America where the nacreous shells of many of them are used for button making

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History and Etymology for Unionidae

New Latin, from Union-, Unio, type genus + -idae

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