Shellfish may be a informal and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, as well as numerous species of molluscs, crustaceans, and echinoderms. though most types of shellfish ar harvested from seawater environments, some ar found in fresh. additionally, a number of species of land crabs ar eaten up, for instance Cardisoma guanhumi within the Caribbean. Shellfish ar among the foremost common food allergens. Despite the name, shellfish don't seem to be really fish, however ar merely water-dwelling animals. Most shellfish ar low on the organic phenomenon and eat a diet composed primarily of plant life and animate being. Molluscs used as a food supply by humans embody several species of clams, mussels, oysters, winkles, and scallops. Some crustaceans that ar unremarkably eaten up ar shrimp, lobsters, crayfish, and crabs. Echinoderms don't seem to be as ofttimes harvested for food as molluscs and crustaceans; but, echinoderm roe is sort of well-liked in several components of the globe, wherever the live delicacy is tougher to move.