The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head, the pereon or thorax, and the pleon or abdomen. The head and thorax may be fused together to form a cephalothorax, which may be covered by a single large carapace.

Crustacean body structure The body of a crustacean can be divided into the head, thorax and abdomen. The head bears the two sets of antennae, mandibles and maxillae (mouth parts). A thorax is the crustacean equivalent of a chest but it is split into numerous segments. Each segment has a pair of legs each leg is usually jointed.