A broad term for all aquatic animals that have a shell of some kind. Shellfish are separated into two basic categoriescrustaceans and mollusks. Crustaceans include crabs, crayfish, lobster and shrimp. Mollusks are divided into three groupsgastropods (also called univalves) such as the abalone and snail; bivalves like the clam and oyster; and cephalopods like octopus and squid. See also fish.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.