No horn, despite the name, and two orange blades either side of the tail.
To about 45 cm, grey-brown with a yellow-orange band across the forehead, a black mask around the eye, orange-yellow lips, and two fixed forward-pointing orange blades on each side of the caudal peduncle. Mature males grow long filaments from the upper and lower lobes of the tail. Unlike most Naso it develops no forehead horn at any size. The closely similar Naso elegans of the Indian Ocean has an orange rather than black dorsal fin and does not reach here.
It browses leafy brown algae, particularly Sargassum and Dictyota, in pairs or small groups along reef edges. It swims steadily and allows a diver to close to a few metres before turning away. Recorded from about 3 to 45 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.