The bristletails constitute the most basal order within the dicondylic insects (Dicondylia). The bristletails are primitively wingless, and share many traits with the jumping bristletails (Archaeognatha), which constitute the sister group to all other insects.
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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 bristletails have so called ametabolous development, which means that they undergo little change from moult to moult except for becoming larger. The bristletails were previously grouped with the jumping bristletails in a larger order, Thysanura. Details in the mouthparts have, however, revealed that the bristletails are more closely related with the winged insects than with the jumping bristletails.