A seashell is the most universally identifiable part of a creature known as a mollusk. Mollusks are invertebrate animals (think of a snail) with an unsegmented, basically symmetrical body, generally consisting of head, foot, visceral hump and mantle. Mollusks are descendants from primitive wormlike creatures inched around in the ooze of primeval seas millions of years ago. As dissolving land masses began to feed salts and chemicals into oceans, the first mollusks digested them and eventually used them to build durable shelters.