mollusc

mollusk

 or mollusc

Representative mollusks. Bivalves have a shell with two halves. Filter feeders, they take in food …

(credit: © Merriam-Webster Inc.)

Any of some 75,000 species of soft-bodied invertebrate animals (phylum Mollusca), many of which are wholly or partly enclosed in a calcium carbonate shell secreted by the mantle, a soft covering formed from the body wall. Between the mantle and the body is the mantle cavity. Mollusks occur in most habitats from the deep sea to high mountains. Living mollusks are usually grouped into eight classes: Gastropoda (see gastropod), Bivalvia or Pelecypoda (see bivalve), Cephalopoda (see cephalopod), Scaphopoda (tusk shells), Aplacophora (Solenogasters), Caudofoveata (sometimes included in the Aplacophora order), Polyplacophora (chitons), and Monoplacophora. Mollusks are economically important as food, and their shells are widely used in jewelry and decorative items.

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mollusc (US), mollusk

any invertebrate of the phylum Mollusca, having a soft unsegmented body and often a shell, secreted by a fold of skin (the mantle). The group includes the gastropods (snails, slugs, etc.), bivalves (clams, mussels, etc.), and cephalopods (cuttlefish, octopuses, etc.)