A division of the class Crustacea, having all the segments of the body usually distinct, gills attached to the feet or organs of the mouth, and the feet fringed with fine hairs. They are generally of small size. 64

Entomostraca is a historical subclass of Crustacea, no longer in technical use, which includes the Phyllopoda, Branchiopoda, Ostracoda, Copepoda, and Pectostraca. The Ostracoda have the body enclosed in a bivalve shell-covering, and normally unsegmented. The Branchiopoda have a very variable number of body-segments, with or without a shield, simple or bivalved, and some of the post-oral appendages normally branchial.