Distinctive Characters: Dorsal fin with 11 spines and 23-26 rays. Anal fin with 3 spines and 20-21 rays. Pectoral fin with 14 rays. Body depth 1.1 in standard length. Dorsal and anal fins elevated posteriorly. Snout small and pointed.
Colour: Ground colour light brown. Dark chevron markings over most of body. Snout-eye band and opercular bar reddish. Caudal fin with broad black triangular or diamond shaped patch bordered with yellow.
Habitat and Biology: Usually found in shallow waters at depths of 2 to 12 m in the close association with branching corals. Feeds on coral polyps.
Distribution: Maldives to Western Indonesia.
Remarks: Chaetodon triangulum is sometimes classified in the genus Gonochaetodon. Differs from C. baronessa Cuvier from the Western Pacific only in caudal colouration. Being a coralivore this species is not easy to maintain in an aquarium.