They're divided into three groups. Gastropods all have a single shell and a single muscle. Gastropods include abalone, limpet, periwinkle, snail, and whelk. Bivalves are soft-bodied mollusks that have two shells hinged together by a strong muscle. Bivalves include clams, mussels, oysters, and scallops.
Cephalopods have tentacles attached to the head, and ink sacs, which serve to evade predators.
The most common cephalopods are octopus, squid, and cuttlefish. All Rights Reserved.