Oniscoidea

a suborder of predominantly terrestrial isopodan crustaceans. The body is 1–50 mm long and dorso-ventrally flattened. There are long antennae and short antennules on the head. Each of the seven somites has a pair of walking legs; the abdomen has five pairs of platelike, biramous respiratory limbs, through whose membranes gas exchange is accomplished (in Oniscoidea found in arid places, these limbs have tracheae). The uropods—the terminal pair of extremities of the abdomen— perform a tactile, supportive, or protective function; sometimes they serve to draw in water to moisten the respiratory surface. The heart is in the abdominal section. Oniscoidea are dioecious. Fertilization is internal; except in a few hermaphroditic parasitic species, the eggs develop in a brood pouch between the walking legs of the mother. Development is without metamorphosis.

There are about 1,000 species of Oniscoidea, distributed throughout the world in moist and warm regions and in dry regions that are rich in CaCO₃. Oniscoidea are particularly numerous in the tropics and subtropics. In the USSR they are found principally in Middle Asia, the Caucasus, and the Crimea. The majority of Oniscoidea are found on the forest floor, in steppe soils, and on limestone. Oniscoidea sometimes injure greenhouse plants and plants cultivated on irrigated land. Most species are beneficial in forests as soil-forming organisms.