Calman, 1904
Peracarida are eumalacostracan crustaceans with a carapace that is never fused to all thoracomeres (the carapace in Amphipoda and Isopoda has been secondarily lost). The antenna typically has a three-segmented protopod. The mandible usually has a lacinia mobilis (an articulated accessory process in adults between molar and incisor processes). The first, rarely the second and third, pair of thoracopods is modified as a maxilliped. The pleoipods do not have an appendix interna. The gills are thoracic or abdominal.
The females have a brood pouch (marsupium) that usually is formed by oostegites, which are medial lamellar outgrowths of the coxae of some of the thoracopods (the Order Thermosbaenacea has no brood pouch but the young are brooded in the carapace).
A true larval form is absent; young hatch as a manca, a pre-juvenile stage lacking the last pair of thoracopods.
The Peracarida include seven orders, those marked below (*) are present in the plankton of the North Sea.
¥ Order Mysidacea *
¥ Order Thermosbaenacea
¥ Order Speleogriphacea
¥ Order Cumacea *
¥ Order Tanaidacea
¥ Order Isopoda *
¥ Order Amphipoda *
[Description after McLaughlin, 1980; Brusca and Brusca, 1990]