Common names: filefish (English), leatherjacket (English), lija (Espanol)
 
Aluterus monoceros (Linnaeus, 1758)


Unicorn filefish,     Unicorn leatherjacket


Body a very compressed elongated oval a long pointed snout, snout profiles of adult - upper convex, lower concave; a small mouth that  opens above center line; teeth moderately strong, six in outer row on top jaw and six or less on outer row on bottom jaw;  gill opening a short slit on side before pectoral base; II dorsal spines, 1st  long and slender, over eye, erectile, can be locked in position by small 2nd  spine; dorsal II, 45-51; anal 47-53; pectoral 14; median fins rays unbranched;  tail fin usually shorter than snout, with straight to slightly concave edge; tail base longer than deep; scales minute, innumerable, equipped with small hairs, cover skin and give it a coarse texture like sand-paper; pelvic fins absent, no scales encasing area where pelvics should be; no patch of enlarged scales above pectoral base; lateral line inconspicuous.


Pale grey to grey-brown; brown spots and blotches on upper side; dorsal and anal pale yellowish brown; tail membranes dark brown; juveniles & sometimes young adults  with network of pale lines enclosing darker spots and blotches.


Size: 76 cm.

Habitat: rocky habitat.

Depth: 0-50 m.

Circumtropical; southern Baja and the lower 1/3 of Gulf of California to Chile; the Revillagigedos, Cocos and Malpelo.