Body elongate, oval; upper and lower body profiles symmetrically convex; forehead without horn; mouth small, protrusible, low on head; teeth small, conical, tips slightly depressed & either smooth or with multiple small points; dorsal fin VI, 27-29; anal II, 27-30; pectoral 17-18 rays; pelvics I, 3; 2 pairs of cutting keels on plates on narrow tail base; tail margin straight, without filaments, concave in juveniles; scales very small, rough; lateral line complete.
Blue-grey to brown above, shading to yellowish brown ventrally; rear margin of operculum and preopercle often dark; tongue black; dorsal olive; tail blue grey, broad olive margin; anal and pelvics yellow-olive; pectoral blue grey, dark margin; courting males can abruptly develop upper head and upper front of body blue, blue lines and spots on front flank.
Size: 75 cm.
Habitat: reefs and rocky shores; juveniles on reef crests in sheltered habitats; adults in midwater around exposed reef fronts.
Depth: 0-150 m; juveniles usually 5-35 m; adults usually 10-40 m.
An Indo-Pacific species recorded as a vagrant at Clipperton and Cocos Islands.