Apterygota

The Apterygota are a small subclass of primitive insects.

They are insects which have never had wings at any time in their evolutionary history. Their first known occurrence in the fossil record is in the Rhynie chert of the Devonian period, ~400 million years ago. While some other insects, such as fleas, also lack wings, these are descended from winged insects, and have lost them during the course of evolution. By contrast, the apterygotes are a primitive group of insects that diverged from other orders before wings evolved.

They have some other primitive traits (features).
The nymphs (younger stages) go through little or no metamorphosis, so they look like the adults. They continue to moult throughout life, with multiple instars (stages) after reaching sexual maturity. All other insects have only a single sexually mature adult stage. Their skin is thin, making them appear translucent. Males deposit sperm packages rather than fertilising the female internally.

Currently, no species are listed as being at conservation risk.

 History of the group 
The classification of the 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 turned out to be paraphyletic. The first three groups formed a monophyletic group, the Entognatha. The Thysanura is more closely related to winged insects.Orders  Thysanura & Archaeognatha thus rendering even the amyocerate apterygotes paraphyletic.

Some think the Collembola are no longer insects at all, but their position is not yet clear.

 Sources 

 Firefly Encyclopedia of Insects and Spiders, edited by Christopher O'Toole, , 2002

Category:Insects