Paraneoptera

Paraneoptera or Acercaria is a superorder of insects which includes lice (bark lice and true lice), thrips, and hemipterans, the true bugs. It also includes the extinct order Permopsocida, known from fossils dating from the Early Permian to the mid-Cretaceous.

All of the insects classified here exhibit various "reductions" or "simplifications" from the primitive body-plan found in typical polyneopterans. Cerci, for example, are entirely absent in all living paraneopterans (Acercaria meaning without cerci). 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.

The mouthparts of the Paraneoptera reflect diverse feeding habits. Some groups are microbial surface feeders, whereas other groups feed on plant or animal fluids.

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.

Here is a simple cladogram showing the traditional relationships with a monophyletic Paraneoptera:

Here is an alternative cladogram showing Paraneoptera as paraphyletic, with Psocodea as sister taxon to Holometabola:

Within Paraneoptera, Psocodea contains the two orders Phthiraptera (lice) and Psocoptera (booklice, barklice or barkflies). However, studies have shown that Phthiraptera is in fact nested deep within Psocoptera, making Psocoptera paraphyletic and an invalid grouping.

Assuming Paraneoptera is monophyletic, here is a more detailed cladogram showing the internal relationships, and how Phthiraptera falls within Psocodea: