The generic term seafood is used to refer to edible marine invertebrate animals with the exception of fish and mammals. The main groups of invertebrates consumed as seafood are bivalves (oysters, mussels, clams, scallops, cockles, etc.), cephalopods (cuttlefish, squid, etc.), gastropods (whelks), crustaceans (crabs, prawns, lobsters, crayfish, crawfish, etc.), and echinoderms (sea urchins). They are commonly divided into two main categories: crustaceans (photo) and mollusks.