shellfish, popular name for certain edible mollusks (see Mollusca), e.g., oysters, clams, and scallops, and for certain edible crustaceans, e.g., crabs, lobsters, and shrimps. All are aquatic invertebrates with shells; they are not fish.

Any aquatic mollusk, crustacean, or echinoderm that has a shell. Oysters, mussels, scallops, and clams rank among the most commercially important. Certain gastropod mollusks, such as abalone, whelk, and conch, are also marketed. The main crustaceans are shrimp, lobster, and crab. Among echinoderms, sea urchins and sea cucumbers are locally popular. After being harvested, all shellfish are highly perishable. Many types are cooked live to protect the consumer against the effects of spoilage.

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