Neohexangitrema spp. (Trematoda: Microscaphidiidae) in Indo-West Pacific Acanthuridae: Richness, distribution, diet and contemporary naming issues

Examination of hundreds of individuals of 32 species of Acanthuridae from the Indo-West Pacific resulted in the collection of trematodes consistent with the genus Neohexangitrema Machida, 1984 from the northern and southern Great Barrier Reef (GBR, Queensland, Australia), Ningaloo Reef (Western Australia), Okinawa (Japan), New Caledonia, and Mo'orea and Rangiroa in French Polynesia. Specimens of Neohexangitrema spp. were primarily collected from two species of Zebrasoma, Z. scopas (Cuvier) and Z. velifer (Bloch), and less frequently from three species of Acanthurus. Specimens from Z. scopas and A. nigricans (Linnaeus) from French Polynesia are morphologically and genetically distinct and here described as N. blairi n. sp. This species appears to represent an unusual case of parasite endemism in French Polynesia. Two other morphotypes occurred, often together, in fishes from at least one of the other localities but not in French Polynesia. The first of these, from Ningaloo Reef, Okinawa, GBR and New Caledonia, is clearly morphologically and genetically distinct and is described as N. phytophagum n. sp. This species frequently has large amounts of undigested algae in the digestive tract and appears to be a herbivore in a herbivore. The second widespread morphotype comprised specimens from Z. scopas and Z. velifer consistent with N. zebrasomatis Machida, 1984 as originally described from Z. velifer from off southern Japan. Molecular analyses (cox1 mtDNA and ITS2 and 28S rDNA) consistently suggest that these new specimens represent two morphologically cryptic species, both infecting Z. scopas and Z. velifer, one only at Ningaloo Reef and the other from the GBR. Neither of these species can presently be positively identified as N. zebrasomatis given the lack of molecular data from the type-locality. We here propose new names for both taxa, N. obscurum n. sp. for the species from the GBR and New Caledonia and N. crypticum n. sp. for the species from Ningaloo Reef. This proposal is made with the explicit understanding that one of the two may well (but will not necessarily) prove a synonym of N. zebrasomatis. This approach draws attention to the developing issue of the management of the names of combinations of cryptic trematode species.