All of the insects classified here exhibit various “reductions” or “simplifications” from the primitive body-plan found in typical polyneopterans.

Other “reductions” occur in wing venation, in the number of tarsal segments (no more than three), only four Malpighian tubules, and only one complex of abdominal ganglia.

[2] Paraneoptera consists of Psocodea (lice), along with their sister clade, the monophyletic grouping Condylognatha that contains Hemiptera (true bugs) and Thysanoptera (thrips).

However, analysis has shown that Psocodea could instead be the sister taxon to Holometabola, which would render Paraneoptera as paraphyletic.

They range in size from 1 millimetre (0.039 in) to around 15 centimetres (5.9 in), and share a common arrangement of sucking mouthparts.

Psocoptera, the bark lice, include 4,400 described species arranged in 3 suborders, Trogiomorpha, Troctomorpha, and Psocomorpha.