(genus Crepidula), any marine snail (family Calyptraeidae, subclass Prosobranchia), in which the humped or flattened shell has a decklike half partition inside. Slipper shells occur worldwide in shallow waters. Adults are fixed to rocks or live within the empty shells of other mollusks. The common Atlantic slipper shell (C. fornicata), often called slipper limpet, is about 4 cm (1.5 inches) long and yellowish; it is abundant from Nova Scotia to Texas and has been introduced on the coast of Europe, where it is a nuisance in oyster beds
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