Unicornfishes of the Subgenus Axinurus (Perciformes: Acanthuridae: Naso), with Description of a New Species

Abstract

The subgenus Axinurus Cuvier of the Indo-Pacific acanthurid genus Naso is unique in having only a single fixed keel-like spine on each side of the caudal peduncle, in contrast to two for other species of Naso. Axinurus consists of three species: N. thynnoides (Valenciennes), N. minor (Smith), and N. caeruleacauda n. sp. Naso thynnoides, which ranges from East Africa to the Caroline Islands and Ryukyus, has IV,28-30 dorsal-fin rays, 13-16 anterior gill rakers, a long oblique groove on side of snout; a median flat area in anterior interorbital and internarial space, and narrow dark bars on the body. Naso minor, named from one specimen from Mozambique, here recorded from Reunion, Indonesia, and the Philippines, is distinct in having V,28 dorsal rays, a short oblique groove on side of snout below nostrils (about equal to length of naked area containing nostrils), a large retrorse spine on side of caudal peduncle of large adults, a yellow caudal fin in life, and a black peduncular basal plate and spine. Naso caeruleacauda n. sp., described herein from two specimens from the Philippines and known from Indonesia from underwater photographs, differs from N. thynnoides in having a straight dorsal profile of snout, a strongly convex interorbital and internarial space, 18-19 anterior gill rakers, a deeper body (2.75-2.8 in SL), and a blue caudal fin in life.