Pthirus is a genus of lice.

There are only two extant species, and they are the sole known members of the family Pthiridae.

[4] Pthirus gorillae infests gorillas,[5] and Pthirus pubis afflicts humans, and is commonly known as the crab louse or pubic louse.

[6] The two species diverged some 3.3 million years ago.

[7] Since 1958 the generic name Pthirus has been spelled with pth rather than phth, despite this being based on a misspelling of the Greek-derived phthirus.