Peracarida Temporal range: upper Devonian–present, | |
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The amphipod Bathyporeia elegans with an egg in its marsupium | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Malacostraca |
Subclass: | Eumalacostraca |
Superorder: | Peracarida Calman, 1904 [1] |
The superorder Peracarida is a large group of malacostracan crustaceans, 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. [2] Peracarida is one of the largest crustacean taxa and includes about 12,000 species. Most members are less than 2 cm (0.8 in) in length, [3] but the largest is probably the giant isopod ( Bathynomus giganteus ) which can reach 76 cm (30 in). The earliest known perecaridian was Oxyuropoda ligioides , a fossil of which has been found dating to the Late Devonian (more than 360 mya) of Ireland. [4]
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. This chamber is where the eggs are brooded, development being direct in most cases. [3] 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 which is often reduced in size and is not fused with the posterior thoracic somites. [5] In some orders, the young hatch at a post-larval, prejuvenile stage called a manca which lacks the last pair of legs. [5] In the underground order Thermosbaenacea, there are no oostergites and the carapace of the female is expanded to form a dorsal marsupium. [3]
There is some disagreement as to which orders should be included within Peracarida. The World Register of Marine Species WoRMS (2023) includes the following 12 orders: [6]
Of these Bochusacea, Ingolfiellida and Stygiomysida have been added since the classification of Martin & Davies (2001). [7] 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, [3] an arrangement that was disputed by Meland and Willassen (2007) since molecular data shows that the three orders are not closely related. [8]
Malacostraca is the second largest of the six classes of pancrustaceans just behind hexapods, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobsters, crayfish, shrimp, krill, prawns, woodlice, amphipods, mantis shrimp, tongue-eating lice and many other less familiar animals. They are abundant in all marine environments and have colonised freshwater and terrestrial habitats. They are segmented animals, united by a common body plan comprising 20 body segments, and divided into a head, thorax, and abdomen.
Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in this pouch and are not free-swimming characterises the order. The mysid's head bears a pair of stalked eyes and two pairs of antennae. The thorax consists of eight segments each bearing branching limbs, the whole concealed beneath a protective carapace and the abdomen has six segments and usually further small limbs.
Eucarida is a superorder of the Malacostraca, a class of the crustacean subphylum, comprising the decapods, krill, and Angustidontida. They are characterised by having the carapace fused to all thoracic segments, and by the possession of stalked eyes.
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.
Eumalacostraca is a subclass of crustaceans, containing almost all living malacostracans, or about 40,000 described species. The remaining subclasses are the Phyllocarida and possibly the Hoplocarida. Eumalacostracans have 19 segments. This arrangement is known as the "caridoid facies", a term coined by William Thomas Calman in 1909. The thoracic limbs are jointed and used for swimming or walking. The common ancestor is thought to have had a carapace, and most living species possess one, but it has been lost in some subgroups.
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 soft-bottoms such as mud and sand, mostly in the marine environment. There are more than 1,500 species of cumaceans formally described. The species diversity of Cumacea increases with depth.
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 is now placed in order Bochusacea, leaving Mictacea with a single species, Mictocaris halope.
Nannastacidae is a family of crustaceans belonging to the order Cumacea. They have no free telson. The endopods of the uropods are present on one segment. There are exopods on the maxillipeds and generally one on pereopods 1–4 in males and 1–2 in females. In the females the second antenna is much shorter than the first. It contains the following genera:
Edriophthalma is a disused peracarid (Malacostraca) classification comprising Isopoda and Amphipoda, first proposed by William Elford Leach in 1815. They have several common features, such as the fact that they both lack a carapace, possess sessile compound eyes, and thoracic coxae fused to their pleurites. Some molecular studies have shown that these are not related. The group has also been known as Acaridea and Arthrostraca.
Phoratopus remex is a species of isopod crustaceans known from only two specimens, and first described in 1925 by Herbert Matthew Hale (1895–1963). It lives on the continental shelf at Encounter Bay and Fowlers Bay, South Australia. It is so unlike all other isopods that it is placed in its own family, Phoratopodidae and suborder, Phoratopidea.
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. Current data indicate that despite their external similarities, the three orders are not closely related, and the taxon Mysidacea is not used in modern taxonomy.
Phylogeny of Malacostraca is the evolutionary relationships of the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members display a great diversity of body forms. Although the class Malacostraca is united by a number of well-defined and documented features, which were recognised a century ago by William Thomas Calman in 1904, the phylogenetic relationship of the orders which compose this class is unclear due to the vast diversity present in their morphology. Molecular studies have attempted to infer the phylogeny of this clade, resulting in phylogenies which have a limited amount of morphological support. To resolve a well-supported eumalacostracan phylogeny and obtain a robust tree, it will be necessary to look beyond the most commonly utilized sources of data.
Platyarthridae is a family of woodlice, containing the following genera:
An oostegite is a large, flexible plate-like flap extending medially from the coxae of the pereiopods in some female crustaceans. It forms part of the marsupium or brood pouch of members of the superorder Peracarida, from the class Malacostraca.
Armadillidae is a family of woodlice, comprising around 80 genera and 700 species. It is the largest family of Oniscidea, and one of the most species-rich families of the entire Isopoda. Most of the armadillidae taxa are not monophyletic. Armadillids generally have a strongly convex body shape, with some rather shallowly convex. Like members of the woodlice family Armadillidiidae, armadillids are capable of enrolling into a sphere (conglobation), and are commonly known as pill bugs. Some species, however, have secondarily lost their conglobation ability. For example, a species exist in which the males lack the inner face of the coxal plates and are therefore unable to conglobate. Armadillids differ from the Armadillidiidae in that the antennae are fully enclosed within the sphere.
The clade Multicrustacea constitutes the largest superclass of crustaceans, containing approximately four-fifths of all described crustacean species, including crabs, lobsters, crayfish, shrimp, krill, prawns, woodlice, barnacles, copepods, amphipods, mantis shrimp and others. The largest branch of multicrustacea is the class Malacostraca.
Siriella is a genus of mysid crustaceans form the family Mysidae, consisting of approximately 90 species. Found in all seas except cold Arctic and Antarctic waters, the genus is most diverse in tropics.
Boreomysinae is a subfamily of large, mostly deep-water oceanic mysid crustaceans from the family Mysidae. The name, which can be translated as "northern mysids", comes from the genus Boreomysis G.O. Sars, 1869, established for Boreomysis arctica from the boreal waters of Atlantic. As more species have been discovered subsequently, the subfamily is considered panoceanic, and includes 38 species from two genera, Boreomysis and Neobirsteiniamysis Hendrickx et Tchindonova, 2020.
Stygiomysida is a small order of malacostracan crustaceans in the superorder Peracarida. It has traditionally been considered part of the order Mysida, but was separated from it on phylogenetic grounds.