Apterygota
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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.
There are no current species at conservation risk.
[edit] History of the concept
The composition and classification of Apterygota changed over time. By the mid 20th century the subclass included four orders (Collembola, Protura, Diplura, and Thysanura). With the advent of a more rigorous cladistic methodology, the subclass was proven paraphyletic. While the first three groups formed a monophyletic group Entognatha (with mouthparts, submerged in a pocket formed by the lateral and ventral parts of the head capsule), Thysanura appeared to be more closely related to winged insects (Pterygota). The most notable synapomorphy proving the monophyly of Thysanura+Pterygota is the absence of intrinsic antennal muscles, connecting the antennomeres in Entognatha, Myriapoda, and Crustacea, for which the whole group is often termed Amyocerata (lacking antennal muscles). Moreover, some entomologists claimed that one of the subgroups within Thysanura (Zygaentoma, or Thysanura in a strict sense) was more closely related to Pterygota than the other (Microcoryphia, or Archaeognatha), thus rendering even the amyocerate apterygotes paraphyletic.
[edit] Sources
- Firefly Encyclopedia of Insects and Spiders, edited by Christopher O'Toole, ISBN 1-55297-612-2, 2002
