In the Branchiopoda the maxillary gland is lodged in the thickness of the shell-fold (when this is present), and, from this circumstance, it often receives the somewhat misleading name of " shell-gland."
The Branchiopoda have a very variable number of body-segments, with or without a shield, simple or bivalved, and some of the postoral appendages normally branchial.
This term was introduced by Thorell in 1864 for the Argulidae, a family which had been transferred to the Branchiopoda by Zenker in 1854, though sometimes before and since united with the parasitic Copepoda.
This zoological term, as now restricted, includes the Branchiopoda, Ostracoda and Copepoda.