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leptostraca
Leptostraca (from the Greek words for ''thin'' and ''shell'')〔(【引用サイトリンク】title=Leptostraca )〕 is an order of small, marine crustaceans. Its members, including the well-studied ''Nebalia'', occur throughout the world's oceans and are usually considered to be filter-feeders. It is the only extant order in the subclass Phyllocarida. They are believed to represent the most primitive members of their class, the Malacostraca, and first appear in the fossil record during the Cambrian period.〔
==Description==
Leptostracans are usually small, typically long, crustaceans distinguished from all other members of their class in having seven abdominal segments, instead of six. Their head has stalked compound eyes, two pairs of antennae (one biramous, one uniramous), and a pair of mandibles but no maxillipeds.〔 The carapace is large and comprises two valves which cover the head and the thorax, including most of the thoracic appendages, and serves as a brood pouch for the developing embryos. The first six abdominal segments bear pleopods, while the seventh bears a pair of caudal furcae, which may be homologous to uropods of other crustaceans.
Leptostracans have gills on their thoracic limbs, but also breathe through a respiratory membrane on the inside of the carapace. The eggs hatch as a postlarval, or "manca" stage, which lacks a fully developed carapace, but otherwise resembles the adult.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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