shellfish

n. invertebrate aquatic animal which has a shell (such as shrimp, oysters, lobster, etc.)

Shellfish is a culinary term for aquatic invertebrates used as food: molluscs, crustaceans, and echinoderms. Both saltwater and freshwater invertebrates are considered shellfish. Shellfish is a misnomer, because these invertebrates are definitely not fish. The term finfish is sometimes used to distinguish ordinary (vertebrate) fish from shellfish.
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Noun
1. meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)
(hypernym) seafood
(hyponym) mussel
(part-holonym) mollusk, mollusc
2. invertebrate having a soft unsegmented body usually enclosed in a shell
(synonym) mollusk, mollusc
(hypernym) invertebrate
(hyponym) scaphopod
(member-holonym) Mollusca, phylum Mollusca
(part-meronym) carapace, shell, cuticle

(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.
  

Synonyms and related words:
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