Carries a long forward-pointing horn that grows with the fish, and changes colour markedly within seconds.
To 60 cm, and it lives to twenty-five years. The appearance changes so much with age that it needs setting out. Adults grow a broad-based tapering horn from the snout that reaches more than half the length of the head in large fish and often projects past the mouth — the longest horn in the genus. Juveniles have no horn at all, just a bump on the forehead that appears at around 10 cm. The body is olive-grey-brown with dark vertical lines and spots, which is the name, and there are spots and lines on the head. There are two fixed plates on the base of the tail, and the tail is square-cut with white margins.
The bluespine unicornfish has a shorter horn and bright blue tail spines. The whitemargin unicornfish has a white ring at the base of the tail. A hornless juvenile can be taken for a sleek unicornfish; check for the body spotting.
The diet changes with age: juveniles graze algae in shallow protected lagoons, adults feed on plankton in midwater over steep outer slopes, often in aggregations. It has been recorded between the surface and 122 m and is usually between 4 and 46 m.
The species name means short snout, which describes the juvenile rather than the adult.
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.