seashell

right|thumb|Seashells washed up on the beach in Valencia, Spain; nearly all are single valves of [[bivalve mollusks, mostly of Mactra corallina]] right|thumb|Hand-picked molluscan seashells (bivalves and [[gastropods) from the beach at Clacton on Sea in England]] thumb|A group of seashells, mostly bivalves in the family Pholadidae thumb|226x226px|Mixed shells on a beach in Venezuela thumb|Hermit crabs inhabiting marine gastropod shells that lived in the [[Persian Gulf]] thumb|A group of beach-worn sea snail shells that vary in size, form and pattern combination.

A seashell (or sea shell), also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. Most seashells are made by mollusks, such as snails, clams, and oysters to protect their soft insides. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have decomposed or been eaten by another organism.