Dorsal fin spines (total): 4-5 Dorsal fin spines (total): 23-28 Anal fin spines: 3 Anal fin spines: 19-24 The adult fish is ovoid in height and flat. The mouth is small, the end position, the upper and lower teeth are large, the teeth are fixed and immovable, flat, and the edges are notched. The hard spines of the dorsal and anal fins are sharp, and the front soft strips are longer than the rear and are umbrella-shaped the tail spine is slightly movable in the front of the caudal stalk, and the caudal fin is truncated. Adult fish body, head and fins are uniformly brownish-black to black, with a green border at the base of the dorsal fin and dark red eyes the caudal spines are white. There is a gray-black band in the center of the side of the body. When the light is dim, the color of the fish body becomes lighter, and the vicinity of the yellow band becomes light brown. The difference between juvenile and adult fish lies in their body color. The body color of juvenile fish is yellowish brown with a darker back part. As he grows, his body color gradually turns black. The shape of the black triangle is exactly the same as the yellow triangle (Zebrasoma flavescens), the only difference is the color. In addition, the difference between Black Triangle and Acanthurus albipectoralis (Acanthurus albipectoralis) is that the body and fins of the Black Triangle are uniformly black, the tail spines are white, and the dorsal and anal fins are tall while the dorsal and anal fins of the white-finned black hanger are The fin rays are not extended, and the caudal and pectoral fins are white, and the tail spine is black, which is easy to distinguish. Body size The maximum body length is 21cm. It inhabits in coral lagoons and sea-facing coral reef areas with a depth of 5-40 meters. It usually lives in the water layer below the surge area. Most live alone or in groups. Mainly feed on silk algae.