Mollusks are soft-bodied invertebrates with bilateral symmetry and usually one or two shells. Their organs are in a fluid-filled cavity; the word mollusks in Latin means "soft". Most of the mollusks live in water but some live on land. There are more than 110,000 species that have been identified.A theoretical, idealized mollusk would crawl on a single flat, muscular foot, and the body would have at least a suggestion of a head at one end and an anus at the other.