Any aquatic animal whose external covering consists of a shell, either testaceous, as in oysters, clams, and other mollusks, or crustaceous, as in lobsters and crabs.

Any aquatic animal whose external covering consists of a shell, for example, oysters, clams, lobsters, and crabs.

An aquatic animal, e.g., clams, oysters, mussels, crabs, lobsters, shrimp, squid and octopus which has a shell; crustaceans or mollusks.

An aquatic animal having a shell or shell-like exoskeleton (i.e. mollusk, crustacean). image