The Ischnocera is a large suborder of lice mostly parasitic on birds but including a large family (the Trichodectidae) parasitic on mammals. The genus Trichophilopterus is also found on mammals (lemurs) but probably belongs to the "avian Ischnocera" and represents a host switch from birds to mammals. Many of the avian Ischnocera have evolved an elongated body shape. This allows them to conceal themselves between the feather shafts and avoid being dislodged during preening or flight.

The taxonomy of the group is in need of revision. Currently four families are recognised but one of these, the Philopteridae, is almost certainly paraphyletic. The families are:

• Heptapsogasteridae
• Goniodidae
• Philopteridae
• Trichodectidae