Two pairs of antennae at some stage in their life cycle.
The body is divided into three parts, a head, thorax and abdomen.
There may be between sixteen and sixty body segments. Although the segments look like rings, the outer shell is continuous. The hard tube-like parts are hardened by deposits of calcium and protein. At the joints the shell is thin and flexible, so that the body may bend.
The Head carries pairs of appendages, usually the antennae, used for sensing its environment and for feeding. The head also carries three pair of appendages that are modified into mouthparts.
Most crustaceans have a carapace, or shell, which folds outwards from the upper surface of the body and covers all or part of the thorax.
The thorax and abdomen have pairs of appendages used for movement such as walking, swimming, climbing. In some cases these appendages are used for respiration and mating.
In advanced crustaceans, such as the prawns, lobsters and crabs, three pair of thoracic appendages help the head mouthparts to handle food.
