Leptostraca

Leptostraca [lep′täs·trə·kə]

(invertebrate zoology)

A primitive group of crustaceans considered as one of a series of Malacostraca distinguished by an additional abdominal somite that lacks appendages, and a telson bearing two movable articulated prongs.

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Leptostraca 

an order of higher marine crustaceans. The body length is 1–4 cm. The thorax and the anterior part of the abdomen are covered with a carapace that is not fused with the thoracic segments; a muscle in front can draw the two parts of the carapace together. The eyes are on short stalks. The thorax has eight pairs of extremities, which have branchial plates. The abdomen in the Leptostraca, in contrast to that of other higher crustaceans, consists of seven segments and ends in a telson with a pair of furcal rami; it bears six pairs of legs, of which the four anterior ones are well developed and serve for swimming. The green glands serve as excretory organs.

The Leptostraca are dioecious. Development does not involve metamorphosis. There are five genera, embracing eight species. The animals are widely distributed. Most are bottom-dwelling, although some live in deep water. In the USSR, Nebalia bipes is common in the Barents Sea. There are two other species in the Sea of Okhotsk and the Bering Sea, including Nebaliposis typica, which inhabits depths of 200–7,000 m in the Bering Sea.