Pygocephalomorpha

The order Pygocephalomorpha is an extinct group of peracarid crustaceans. Pygocephalomorpha appeared in the Late Devonian, were abundant from the Carboniferous era until their extinction in the Early Permian era.
This group constituted part of the freshwater and aquatic crustacean assemblages. The carapace is relatively axially shortened, with a prominent gastric region. Laterally, a cervical groove is visible, with carapace margins which is defined by an acute spine or process, including a somewhat well developed branchiostegites"

Families

The order contains extinct five families, and seven genera incertae sedis: