The superorder Peracarida is a large group of
crustaceans, having members in marine, freshwater, and terrestrial habitats. They are defined by 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), of a
carapace which is often reduced in size and is not fused with the posterior thoracic somites. In all orders except the Thermosbaenacea, where the carapace is used to brood eggs, the basalmost segments of the
legs bear thin flattened plates (oostegites) which enclose a ventral brood pouch, known as a
marsupium. The young hatch at a post-larval, prejuvenile stage called a manca which lacks the last pair of legs.
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