Sargassum fish

Histrio histrio, a strange-looking fish, blends well with its surroundings in its seaweed habitat. It is laterally compressed and its length can reach 20 cm (7.9 in). The colour of the body and the large oral cavity is very variable, but is usually mottled and spotted yellow, green, and brown on a paler background, and the fins often have several dark streaks or bands. The fish can change colour rapidly, from light to dark and back again. The body and the fins are covered with many weed-like protrusions, but other than these, the skin is smooth without dermal spines. The dorsal fin has three spines and 11–13 soft rays. The front spine is modified into a slender growth on the upper lip known as an illicium, which is tipped by a fleshy lump, the esca. The junction between the head and body is indistinct because no gill slits are present; the gills open as pores near the base of the pectoral fins. The anal fin has no spines and seven to 13 soft rays. The pelvic fins are large and the pectoral fins have 9-11 rays and are stalked and able to grip objects. The outer rays of the tail fin are simple, but the central rays are forked.