Slender suckerfish

The slender suckerfish or lousefish (Phtheirichthys lineatus) is a rare species of remora found around the world in tropical and subtropical seas.

The body of the slender suckerfish is elongated, with long dorsal and anal fins. The dorsal fin rays number 29-33, the anal fin rays 29-34, and the pectoral fin rays 18-21. The adhesive disk atop the head is small, length 18-28% of the standard length, with 9-11 lamellae. The caudal fin is paddle-shaped. 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. The fins are blackish, with the outer portions of the longer dorsal and anal fin rays and the margins of the outer caudal fin rays light. It usually reaches 34 cm (13 in) in total length (TL), but has been reported up to 76 cm (30 in) TL. The sucker disk is fully developed in 50-mm individuals.