The superorder Peracarida is a large group of

malacostraca Malacostraca is the second largest of the six classes of pancrustaceans behind insects, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crab ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or ''marsupium'', formed from thin flattened plates ( oostegites) borne on the basalmost segments of the legs. Peracarida is one of the largest crustacean taxa and includes about 12,000 species. Most members are less than in length, but the largest is probably the giant isopod ('' Bathynomus giganteus'') which can reach . The earliest known perecaridian was '' Oxyuropoda ligioides'', a fossil of which has been found dating to the Late

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

(more than 360 mya) of Ireland.

Characteristics

The most obvious characteristic of the group is the marsupium in females. This brood pouch is enclosed by the large, flexible oostergites, bristly flaps which extend from the basal segments of the thoracic appendages, which form the floor of a chamber roofed by the animal's

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

. This chamber is where the eggs are brooded, development being direct in most cases. Other characteristics include the possession of a single pair of maxillipeds (rarely 2–3), of mandibles with an articulated accessory process between the molar and incisor teeth in the adults (called the ''lacinia mobilis''), and of a

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

which is often reduced in size and is not fused with the posterior thoracic

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryogenesis, embryonic stage of somitogenesis, along the head-to-tail axis in segmentation (biology), segmented animals. ...

s. In some orders, the young hatch at a post-larval, prejuvenile stage called a '' manca'' which lacks the last pair of legs. In the underground order

Thermosbaenacea Thermosbaenacea is a group of crustaceans that live in thermal springs in fresh water, brackish water and anchialine Habitat (ecology), habitats. They have occasionally been treated as a distinct superorder (Pancarida), but are generally consider ...

, there are no oostergites and the carapace of the female is expanded to form a dorsal marsupium.

Orders

There is some disagreement as to which orders should be included within Peracarida. The

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...

WoRMS (2023) includes the following 13 orders: *

Amphipoda Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...

Latreille, 1816 * Bochusacea Gutu & Iliffe, 1998 *

Cumacea Cumacea is an order (biology), order of small marine crustaceans of the superorder Peracarida, occasionally called hooded shrimp or comma shrimp. Their unique appearance and uniform body plan makes them easy to distinguish from other crustaceans. ...

Krøyer, 1846 * Ingolfiellida Hansen, 1903 *

Isopoda Isopoda is an order of crustaceans. Members of this group are called isopods and include both aquatic species and terrestrial species such as woodlice. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed l ...

Latreille, 1817 *

Lophogastrida Lophogastrida is an Order (biology), order of malacostracan crustaceans in the superorder Peracarida, comprising shrimp-like animals that mostly inhabit the relatively deep pelagic waters of the oceans throughout the world. Most lophogastridan s ...

Sars Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the virus SARS-CoV-1, the first identified strain of the SARS-related coronavirus. The first known cases occurred in November 2002, and the ...

, 1870 * Mictacea Bowman et al., 1985 *

Mysida Mysida is an order (biology), order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a Brood pouch (Peracarida), brood pouch or "marsupium" in females. The ...

Haworth Haworth ( , , ) is a village in West Yorkshire, England, in the Pennines south-west of Keighley, 8 miles (13 km) north of Halifax, west of Bradford and east of Colne in Lancashire. The surrounding areas include Oakworth and Oxenhop ...

, 1825 *† Pygocephalomorpha Beurlen, 1930 * Spelaeogriphacea Gordon, 1957 * Stygiomysida Tchindonova, 1981 *

Tanaidacea The crustacean order Tanaidacea (known as tanaids) make up a minor group within the class (biology), class Malacostraca. There are about 940 species in this order. Description Tanaids are small, shrimp-like creatures ranging from in adult size, ...

Dana, 1849 *

Monod, 1927 Of these Bochusacea, Ingolfiellida and Stygiomysida have been added since the classification of Martin & Davies (2001). Ruppert et al. (2004) excluded Thermosbaenacea and placed it in a separate order, Pancarida. They also still kept Lophogastrida, Mysida and Pygocephalomorpha in a single order Mysidacea, an arrangement that was disputed by Meland and Willassen (2007) since molecular data shows that the three orders are not closely related.

References

External links

* * {{Authority control Malacostraca Arthropod superorders