Diagnosis
Carapace often relatively large, up to 30mm, with or without an anterior rostral incisure. Ventral margin often convex. Calcification of outer lamellae of the carapace usually weak or even absent. Ornamentation usually weak or lacking. Adductor muscle scars varied. Between five and seven pairs of appendages. Antenna biramous; exopodite with 7-9 articulated podomeres, endopodite reduced with few podomeres. Maxilla without a branchial plate. Fifth limb with an epipodial appendage (branchial plate). Sixth and seventh limbs varied (Myodocopina and Halocypridina) or absent (Cladocopina). Furca triangular, lamelliform and armed with strong marginal chelate setae. The anus opens anteriorly and ventrally to the furca (Kornicker, 1975).
Marine; many are truly pelagic in the open ocean, while others are essentially benthic swimmers and may be encountered in shallow sublittoral waters.