UNICORNFISHES OF THE SUBGENUS AXINURUS (PERCIFORMES, ACANTHURIDAE, NASO), WITH DESCRIPTION OF A NEW SPECIES

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. m inor (Smith), and N. caeruleacauda n. sp. Naso thynnoides, which range s from East Africa to the Caroline Islands and Ryukyus, has IV,28-30 d orsal-fin rays, 13-16 anterior gill rakers, a long oblique groove on s ide of snout; a median flat area in anterior interorbital and internar ial space, and narrow dark bars on the body. Naso minor, named from on e specimen from Mozambique, here recorded from Ri union, Indonesia, an d the Philippines, is distinct in having V,28 dorsal rays, a short obl ique groove on side of snout below nostrils (about equal to length of naked area containing nostrils), a large retrorse spine on side of cau dal peduncle of large adults, a yellow caudal fin in life, and a black peduncular basal plate and spine. Naso caeruleacauda n. sp., describe d herein from two specimens from the Philippines and known from Indone sia 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 SE), and a blue caudal fin in life.