New Gyrodactylus Species (Monopisthocotyla: Gyrodactylidae) on Freshwater Goby Rhinogobius giurinus (Perciformes: Gobiidae) in China.

PURPOSE: Monogeneans of the genus Gyrodactylus von Nordmann, 1832 are common parasites of fish. In this study, we describe a new species from the goby Rhinogobius giurinus in China, based on morphological and molecular data. METHODS: Gyrodactylids were collected from R. giurinus in three provinces (Hubei, Hunan and Yunnan) of China, stained and examined under light microscopy. Morphological descriptions were prepared and compared with the related species through detailed drawings and precise point-to-point measurements. The ribosomal internal transcribed spacer (ITS; ITS1–5.8 S–ITS2), 18 S rDNA and mitochondrial cox1 markers were sequenced for interspecific and intraspecific comparison and phylogenetic analysis. RESULTS: Gyrodactylus xiaehu n. sp., is characterized by its opisthaptoral hard parts morphology, including a broad heel with a thin-pointed marginal hook sickle, a long ventral bar process, and a heavily curved hamulus root. These features are consistent with the G. orecchiae group species parasitizing a broad range of fishes in marine environments, evidenced by the ITS rDNA phylogenetic analyses. CONCLUSION: The new species is a broadly distributed freshwater species that maintains a close evolutionary relationship with marine lineages, suggesting the marine-to-freshwater history of its host.