The one with the actual horn, which grows forward past the mouth in adults.
To about 70 cm, olive to blue-grey with two bright blue fixed blades on each side of the caudal peduncle and, in adults, a horn projecting forward from the forehead that can extend beyond the mouth. Juveniles have no horn and are easily taken for another surgeonfish. The horn’s function is not settled; it is present in both sexes and does not appear to be used in fighting.
It browses leafy brown algae on reef crests and upper slopes, often where surge is strong, in loose groups. Adult males develop long tail filaments. It is one of the larger herbivores on these reefs and among the more heavily fished. Recorded from about 3 to 40 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.