Why was the former insect order Thysanura replaced by Archaeognatha and Zygentoma?

The former insect order Thysanura was considered a single group of primitive wingless insects within the subclass Apterygota. However, modern entomological classification has replaced it with the orders Archaeognatha and Zygentoma to reflect more accurate evolutionary relationships and distinct morphological differences.12

The division is based on significant anatomical criteria, most notably the structure of the mouthparts. While both groups are ectognathous (having external mouthparts), they are differentiated by several key features, including:

• Archaeognatha: Commonly known as bristletails, these insects possess compound eyes, three ocelli, and a long median tail filament accompanied by lateral cerci.2
• Zygentoma: This order, which includes silverfish and firebrats, features flattened bodies and unjointed abdominal styli, with compound eyes that may be present or absent.21

By separating these groups, taxonomists have refined the classification of Insecta to better distinguish between these lineages and other hexapods, such as proturans, collembolans, and diplurans, which are now often treated as independent classes rather than part of the traditional Apterygota.21