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The name Apterygota is sometimes applied to a subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history. Their first known occurrence in the fossil record is during the Devonian period, 417–354 million years ago. The nymphs (younger stages) go through little or even no metamorphosis, hence they resemble the adult specimens. Their skin is thin, making them appear translucent. Currently, no species are listed as being at conservation risk. == Characteristics == The primary characteristic of the apterygotes is they are primitively wingless. While some other insects, such as fleas, also lack wings, they nonetheless descended from winged insects but have lost them during the course of evolution. By contrast, the apterygotes are a primitive group of insects that diverged from other ancient orders before wings evolved. Apterygotes, however, have the demonstrated capacity for directed, aerial gliding descent from heights. It has been suggested by researchers that this evolved gliding mechanism in apterygotes might have provided an evolutionary basis from which winged insects would later evolve the capability for powered flight.〔Yanoviak SP, Kaspari M, Dudley R. (2009). Gliding hexapods and the origins of insect aerial behaviour. Biol Lett. 5(4):510-2. PMID 19324632〕 Apterygotes also have a number of other primitive features not shared with other insects. Males deposit sperm packages, or spermatophores, rather than fertilizing the female internally. When hatched, the young closely resemble adults and do not undergo any significant metamorphosis, and lack even an identifiable nymphal stage. They continue to molt throughout life, undergoing multiple instars after reaching sexual maturity, whereas all other insects undergo only a single instar when sexually mature. Apterygotes possess small appendages, referred to as "styli", on some of their abdominal segments, but play no part in locomotion. They also have long, paired abdominal cerci and a single median, tail-like caudal filament, or telson. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Apterygota」の詳細全文を読む スポンサード リンク
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