Common on sandy reefs where it feeds upon algal film growing on sand.  Olive or dark brown with brown pectoral fins, a white band on the caudal peduncle, and a long black caudal spine.  Mutant missing its tail at Hanauma Bay was fully grown and did not appear to be impaired since surgeonfishes rely mostly on pectoral fins for locomotion.  Attains 17 inches.  Hawai‘i and the Indo-Pacific.  Formerly confused with Acanthurus mata.