Mollusk

Mollusk, any of many soft-bodied invertebrate animals (phyllum Mollusca), typically having a shell into which the body can withdraw. Mollusks constitute the second largest phylum of invertebrates. They include slugs and snails, limpets, winkles, clams, mussels, and oysters, as well as octopuses and squids. Mollusks have adapted to niches in the sea, in fresh water, and on land. Major groups of mollusks include bivalves, cephalopods, chitons, and gastropods.