The jumping bristletails constitute the most basal insect order, and give a good indication of what the earliest insects must have looked like.

Jumping bristletails are small, elongate insects with body covered with scales. The antennae are long, and the tip of the abdomen bears three long, multisegmented filaments. The jumping bristletails are primitively wingless and have so called ametabolous development, which means that they undergo little change from moult to moult except for becoming larger. The jumping bristletails were previously grouped with the bristletails (Zygentoma) in a larger order, Thysanura. Details in the mouthparts have, however, revealed that the true bristletails are more closely related with the winged insects than with the jumping bristletails.