Archaeognatha in the context of "Apterygota"

Pterygota (/ˌtɛrəˈɡoʊtə/ terrə-GOH-tə Ancient Greek: πτερυγωτός, romanized: pterugōtós, lit. 'winged') is a subclass of insects that includes all winged insects and groups which lost them secondarily.

Pterygota group comprises 99.9% of all insects. The orders not included are the Archaeognatha (jumping bristletails) and the Zygentoma (silverfishes and firebrats), two primitively wingless insect orders. Unlike Archaeognatha and Zygentoma, the pterygotes do not have styli or vesicles on their abdomen (also absent in some zygentomans), and with the exception of the majority of mayflies, are also missing the median terminal filament which is present in the ancestrally wingless insects.

Ametabolism is a type of growth or life cycle in insects in which there is slight or no metamorphosis, only a gradual increase in size. It is present only in primitive wingless insects: the orders Archaeognatha and Zygentoma.

Zygentoma are an order in the class Insecta, and consist of about 550 known species. The Zygentoma include the silverfishes or fishmoths, and the firebrats. A conspicuous feature of the order are the three long caudal filaments. The two lateral filaments are cerci, and the medial one is an epiproct or appendix dorsalis. In this they resemble the Archaeognatha, although the cerci of Zygentoma, unlike in the latter order, are nearly as long as the epiproct.

Until the late twentieth century the Zygentoma were regarded as a suborder of the Thysanura, until it was recognized that the order Thysanura was paraphyletic, thus raising the two suborders to the status of independent monophyletic orders, with Archaeognatha as sister group to the Dicondylia, including the Zygentoma.

The Entognatha, from Ancient Greek ἐντός (entós), meaning "inside", and γνάθος (gnáthos), meaning "jaw", are a class of wingless and ametabolous arthropods, which, together with the insects, makes up the subphylum Hexapoda. Their mouthparts are entognathous, meaning that they are retracted within the head, unlike the insects. Entognatha are apterous, meaning that they lack wings. The class contains three orders: Collembola (springtails, 9000 species), Diplura ("two-tail", 1000 species) and Protura ("first-tail", 800 species). These three groups were historically united with the now-obsolete order Thysanura to form the subclass Apterygota, but it has since been recognized that these orders might not be closely related, and Entognatha and Apterygota are now both considered to be paraphyletic groups.

Thysanura is the now deprecated name of what was, for over a century, recognised as an order in the class Insecta. The two constituent groups within the former order, the Archaeognatha (jumping bristletails) and the Zygentoma (silverfish and firebrats), share several characteristics, such as of having three long caudal filaments, the lateral ones being the cerci, while the one between (telson) is a medial cerciform appendage, specifically an epiproct. They are also both wingless, and have bodies covered with fine scales, rather like the scales of the practically unrelated Lepidoptera. In the late 20th century, it was recognized that the two suborders were not sister taxa, therefore Thysanura was paraphyletic, and the two suborders were each raised to the status of an independent monophyletic order, with Archaeognatha sister taxon to the Dicondylia, including the Zygentoma.

Although the group Thysanura is no longer recognized, the name still appears in some published material. Another name used to separate the two groups from winged insects is Apterygota.