Dorsal-fin rays IV-V, 28-30 ; anal-fin rays II, 27-28 ; pectoral-fin rays 17; pelvic-fin rays I,3. Juveniles plain gray and a white peduncle. Adult males with a long anterior to eye which may extend before mouth; adult females with only a prominent bump before eye; adult with two peduncular plates; with a sharp keel ending in a forward-projecting point; head and upper half of body gray, the lower half whitish to pale yellowish, the demarcation irregular; often with a few small pale blue spots behind eye; large males with dark bars on lower side.
habitats
Occurs in deep coastal to outer reef slopes, usually in small groups but occasionally in large schools. Adults seen in shallow reef aeras but usually difficult to approach underwater. Feeds on benthic algae.
Distribution
Indo-Pacific: East Africa to the Marquesan and Society islands; north to the Ryukyus, south to Vanuatu; Palau and Guam in Micronesia.
Taiwan: South, Lyudao.
Cuvier, G. etc. 1835 
