What is a crustacean?
A crustacean is an arthropod, meaning it is an animal that has an external skeletal support system and jointed legs and other appendages. Crustaceans differ from other arthropods in having two pairs of sensory appendages called antennae (insects have only one pair, and chelicerates, such as spiders and scorpions, have none). Unlike insects, which are nearly all recognizable in having three distinct body regions (head, thorax, and abdomen) and six legs, crustaceans come in all shapes and sizes, and can have many different legs and other appendages. Crustaceans are primarily marine (living in or near the sea), but many also inhabit freshwater and terrestrial habitats. Their habitats range from the deep-sea to the highest mountain lakes, and from shallow warm waters of the tropics to the deepest and coldest ocean basins. More than 70,000 species of crabs, shrimps, lobsters, and their close relatives have been described — more than twice the number of all amphibians, reptiles, birds, and m
