Brusca, Richard C. Arizona-Sonora Desert Museum, Tucson, Arizona.
Last reviewed:March 2021
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A large crustacean superorder. Members of the superorder Peracarida, commonly termed peracarids, comprise a major category of eumalacostracan crustaceans (subclass Eumalacostraca, class Malacostraca, subphylum Crustacea, phylum Arthropoda). The most notable and numerous peracarids are isopods (members of the order Isopoda) and amphipods (members of the order Amphipoda) [Fig. 1]. Peracarids are defined as having the following characteristics: a telson (posteriormost body segment) without appendages; one pair (rarely two or three pairs) of maxillipeds (thoracic appendages modified as mouthparts); mandibles (primary jaws) with articulated accessory processes between the molar and incisor teeth, called the lacinia mobilis, in adults; a carapace, when present, that is not fused with posterior thoracic segments and that is usually reduced in size; basalmost leg segments of the thorax with unique, thin, flattened ventral plates (oostegites) that enclose a ventral brood pouch (marsupium), except in members of the order Thermosbaenacea (which instead use the carapace to brood embryos); and having the young hatch as a prejuvenile stage called a manca, which lacks the last pair of legs (that is, no free-living larvae occur in peracarids). Approximately 12,000 species of peracarids are known. See also: Arthropoda; Crustacea; Eumalacostraca; Malacostraca
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