Crustaceans are the hard-shelled arthropods that include lobsters, crabs, shrimps, prawns, crayfish, and langoustines — most living in the sea, with some in fresh water or on land. Their bodies are armoured in a chitin-and-calcium exoskeleton that they shed and regrow as they grow, and their sweet, delicate flesh sits inside that shell in segmented sections. As food they are prized for lean protein, iodine, selenium, and the long-chain omega-3 fatty acids found especially in cold-water species, though they are also among the major food allergens and must be clearly declared. Their muscle is highly perishable: enzymes and bacteria spoil them fast, so the industry freezes, cooks, or ices them immediately after catch. From bisque to tempura to a simple boiled shrimp, crustaceans anchor some of the most valued dishes in world seafood cookery.