Class of Crustacea - Malacostraca

Malacostraca involves most of the larger forms such as crabs, lobsters, shrimps etc. and constitute the majority of crustacean species. The cephalic region is formed by using the fusion of five segments; the trunk region contains five thoracic and six abdominal segments. Additionally, a postabdominal telson forms part of the tail fin. A carapace that is covering the thorax may or may not be present. The thoracic appendages called pereopods or walking legs have well developed endopodite employed for crawling and prehension. The thoracic legs have gills, generally modified epipodites. In many malacostracans, first pair of thoracic appendages are modified into maxillipeds employed for feeding. The first five pairs of abdominal appendages called pleopods are the swimming legs. Besides swimming, they may also be used for burrowing carrying eggs in females and frequently for gas exchange. In males the first pair of abdominal appendages are changed as copulatory organs.