Masked Swallowtail Angelfish

Genicanthus semifasciatus is sexually dichromatic; the males and females show different colouration and patterning. The male has a yellow head and anterior flanks with a darker yellow dorsal area which is marked with dusky vertical bars. The dorsal area of females is greyish brown and white ventrally, with a yellow margin to the dorsal fin with a black head and caudal fin, and black on the head and tail. In both sexes the forked tail narrows at its base to create a "swallow tail". The dorsal fin contains 15 spines and 15–16 soft rays while the anal fin has 3 spines and 17 soft rays. This species attains a maximum total length of 21 centimetres (8.3 in).

Genicanthus semifasciatus is found in the Western Pacific Ocean. Here it is found from southern Japan, including the Ogasawara Islands, the Izu Islands and the Ryukyu Islands, to the northern Philippines.