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.
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."
Parthenogenesis is prevalent in the Branchiopoda and Ostracoda, often in more or less definite seasonal alternation with sexual reproduction.
This zoological term, as now restricted, includes the Branchiopoda, Ostracoda and Copepoda.
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.