(n.) 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.

Dungeness crab Japanese crab blue point clam coquillage crab crawdad crawfish crayfish langouste limpet littleneck clam lobster mussel oyster periwinkle prawn quahog scallop shrimp snail soft-shell crab steamer whelk