The slender suckerfish or lousefish (Phtheirichthys lineatus) is a rare species of remora found around the world in tropical and subtropical seas,[3] in areas like the Atlantic, Pacific, and Indian Ocean, from depths from 1 to 100 meters deep.

[1] The body of the slender suckerfish is elongated, with long dorsal and anal fins.

The head and body are pale, dark brown, or blackish.

Larger specimens have a distinctive dark brown stripe running along the side of the body, bordered by narrower white stripes above and below.

[6] With the smallest adhesive disk amongst the remoras, the slender suckerfish is not strongly host-dependent and can be encountered free-swimming or attached to inanimate objects.