The superorder Peracarida is a large group of
malacostraca
Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobst ...
n
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
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 (
oostegite An oostegite is a large, flexible plate-like flap extending medially from the coxae (first segments) of the pereiopods (thoracic appendages) in some female crustaceans. It forms part of the marsupium or brood pouch of members of the superorder Pe ...
s) borne on the basalmost segments of the
legs
A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ...
. 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
A giant isopod is any of the almost 20 species of large isopods, crustaceans distantly related to shrimp and crabs, which are decapods, in the genus ''Bathynomus''. They are abundant in the cold, deep waters of the Atlantic, Pacific, and Indian ...
(''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 geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
(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 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 blood vessels from injury. Sh ...
. 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
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
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 Dorsum (biology), 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 tor ...
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 embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide in ...
s. In some orders, the young hatch at a post-larval, prejuvenile stage called a ''manca
The manca (plural: ''mancae'') is the post- larval juvenile in some crustaceans. The manca stage is the defining characteristic of a clade called Mancoida which comprises all the member of the Peracarida except the Amphipoda. Mancae closely rese ...
'' 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 habitats. They have occasionally been treated as a distinct superorder (Pancarida), but are generally considered to belong to t ...
, 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. Martin & Davies include the following eleven orders:
*Amphipoda
Amphipoda is an 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 9,900 amphipod species so far desc ...
Latreille, 1816
*Cumacea
Cumacea is an 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. They live in so ...
Krøyer, 1846
*Isopoda
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...
Latreille, 1817
*Lophogastrida
Lophogastrida is an 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 species are l ...
Sars
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''sever ...
, 1870
*Mictacea
Mictacea is a monotypic order of crustaceans. It was originally erected for three species of small shrimp-like animals of the deep sea and anchialine caves. They were placed in two families, the Mictocarididae and Hirsutiidae, but Hirsutiidae ...
Bowman, Garner, Hessler, Iliffe & Sanders, 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 the City of Bradford, West Yorkshire, England, in the Pennines, south-west of Keighley, west of Bradford and east of Colne in Lancashire. The surrounding areas include Oakworth and Oxenhope. Nearby villages includ ...
, 1825
*†Pygocephalomorpha
The order Pygocephalomorpha is an extinct group of peracarid crustaceans. Pygocephalomorpha were abundant from the Carboniferous until their extinction in the Permian.
Families
The order contains extinct five families, and seven genera ''incert ...
Beurlen, 1930 (only known from fossil remains)
* Spelaeogriphacea Gordon
Gordon may refer to:
People
* Gordon (given name), a masculine given name, including list of persons and fictional characters
* Gordon (surname), the surname
* Gordon (slave), escaped to a Union Army camp during the U.S. Civil War
* Clan Gordon, ...
, 1957
*Tanaidacea
The crustacean order Tanaidacea (known as tanaids) make up a minor group within the class Malacostraca. There are about 940 species in this order.
Description
Tanaids are small, shrimp-like creatures ranging from in adult size, with most specie ...
Dana, 1849
*Thermosbaenacea
Thermosbaenacea is a group of crustaceans that live in thermal springs in fresh water, brackish water and anchialine habitats. They have occasionally been treated as a distinct superorder (Pancarida), but are generally considered to belong to t ...
Monod, 1927
but Ruppert, Fox and Barnes exclude Thermosbaenacea and place it in a separate order, Pancarida. They also place Lophogastrida, Mysida and Pygocephalomorpha in a single order, Mysidacea
The Mysidacea is a group of shrimp-like crustaceans in the superorder Peracarida, comprising the two extant orders Mysida and Lophogastrida and the prehistoric Pygocephalomorpha
The order Pygocephalomorpha is an extinct group of peracarid c ...
. This arrangement is disputed by Meland and Willassen who found that molecular data
In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succi ...
shows that the three orders are not closely related.
References
External links
*
*
{{Authority control
Malacostraca
Arthropod superorders