Crabs are decapod crustaceans of the infraorder Brachyura, characterized by their short, tail-like abdomen, which is usually hidden under the thorax. They inhabit oceans, freshwater, and land, and are covered by a thick exoskeleton primarily made of chitin. Crabs have five pairs of legs, including pincer claws, and breathe through gills on their underside. They vary in size from the tiny pea crab to the large Japanese spider crab, which can have a leg span of up to 4 meters. Some similar-looking crustaceans, like king and porcelain crabs, are not true crabs but have evolved similar features through carcinisation.
