Chaetodon ulietensis is one of the 88 members of the genus Chaetodon, which together with 11 additional genera make up the butterflyfishes family (Chaetodontidae) in which a total of 129 species are currently described. This species lives in the tropical waters of the Pacific Ocean, and in some areas bordering the Pacific Ocean and the Indian Ocean. They range from the Cocos Islands to the Tuamotu Islands and Japan. They are generally found in waters up to 20-30 meters deep and associated with reef channels with high current presence.
The body of Chaetodon ulietensis can reach up to 15 cm maximum total length. The body shape is oval, laterally compressed and with a pointed rostrum formed by a convex dorsal rostral profile and a concave ventral rostral profile. The dorsal fin has 12 spines with closely spaced membranes between them. Generally the spiny region of the dorsal and anal fins are retracted, and only the soft ray portions, which are much more developed, are extended. The dorsal fin is complemented by 23-25 soft rays. The anal fin has 3-4 spines and 19-21 soft rays. The ventral and pectoral fins have only soft rays, and the caudal fin is truncated in shape.
The livery of Chaetodon ulietensis has black vertical lines on a white background. They have a black spot on the caudal peduncle, as well as a black stripe across the eye, and two blackish, fuzzy-edged spots on the dorsum. The back of the body, including the dorsal and anal fin region are bright yellow.
In appearance, Chaetodon ulietensis resembles the species Chaetodon falcula, although the latter is somewhat larger (up to 20 cm) and differs in that the two dorsal spots are less diffuse than in the case of Chaetodon ulietensis.
It is common to observe the specimens of Chaetodon ulietensis in isolation, although it is also possible to observe them in the form of small groups. During the reproductive season, pairs are formed that will release eggs and sperm into the water column, so that fertilization occurs and the dominant currents spread their offspring over a vast territory.