This species is characterized by the following: body depth vary from about 2.0 in SL (in subadults) to 2.4-2.6 (adults) in SL; with a tapering, bony, horn on forehead of adults projecting anteriorly at level of eye but not extending in front of mouth (horn first as a bump on forehead at a length of about 12 cm); dorsal profile from snout to horn straight, angle of about 45°; 2 peduncular plates with well-developed forward-curving knife-like spines; emarginate caudal fin when young, truncate with filamentous lobes in adult; males apparently with longer horn, larger peduncular keels and longer caudal filaments than females of the same size; body yellowish to olivaceous gray dorsally, paler ventrally, with blue peduncular plates and keel spines; lips whitish or blue; blue area is sometimes present around pectoral fin; dorsal and anal fins yellowish with narrow blue margins; caudal fin orangish basally, shading to gray, with a broad, pale greenish posterior border and caudal filaments are edged in blue; one transient color phase is a blotchy pale greenish zone below the spinous portion of dorsal fin that narrows and ends beneath the pectoral fin (Ref. 27362).