[1][2] Their mouthparts are entognathous, meaning that they are retracted within the head, unlike the insects.

[1] Entognatha are apterous, meaning that they lack wings.

[5][1][2] These three groups were historically united with the now-obsolete order Thysanura to form the class Apterygota, but it has since been recognized that the hexapodous condition of these animals has evolved independently from that of insects, and independently within each order.

[6] The orders might not be closely related, and Entognatha is now considered to be a paraphyletic group.

Their mouthparts are enclosed within a pouch in the head capsule, called the gnathal pouch, so only the tips of the mandibles and maxillae are exposed beyond the cavity.