A crustacean within the Malacostraca: Peracarida. All have a well-developed carapace which is fused dorsally with at least the first three thoracic somites and which overhangs the sides to enclose a branchial cavity. The telson may be free or may appear lacking because it is fused with the last abdominal somite. Eyes are sessile and, except for a few genera, are coalesced in a single median organ or wholly wanting. There are eight pairs of thoracic appendages, the first three modified as maxillipeds and the last five as peraeopods. The first maxillipeds bear an epipodite forming a respiratory organ with a forward-directed siphon and a posterior part carrying branchial lobes. Natatory exopodites may be present on the third maxillipeds and the first four pairs of peraeopods or some of them. The uropods are styliform. There is no free larval stage. In the few species whose life history has been investigated there are five to seven molts after release from the brood pouch.