Gyrodactylus nigeri n. sp. (Monogenea: Gyrodactylidae) parasitic on Yunnanilus niger (Cypriniformes: Nemacheilidae) from Yunnan Province, Southwest China

To investigate the infection of fish of the genus <i>Yunnanilus</i> by <i>Gyrodactylus</i> (Monogenea) parasites in the karst region of Yunnan (Southwest China), <i>Gyrodactylus</i> individuals were obtained from the rare and vulnerable host black loach <i>Yunnanilus niger</i>. Based on morphology and partial internal transcribed spacer (ITS) sequence data, we identified and described a new species <i>Gyrodactylus nigeri</i> n. sp. Obtained from the fins of <i>Y. niger</i> from Yunnan Province, Southwest China. Of all available gyrodactylid sequences, the ITS fragment obtained has the highest similarity (88.3%) to the same part of the rDNA of <i>Gyrodactylus kobayashii</i>. The prevalence and mean intensity were 100% and 11.9, respectively. The morphological comparison of the similar haptoral structures revealed slight differences between the new species and the five <i>Gyrodactylus</i> species found in the hosts of Nemacheilidae, and the marginal hooks were compared with the 18 <i>Gyrodactylus</i> species found in the hosts of Nemacheilidae. In particular, <i>G</i>. <i>nigeri</i> n. sp. has robust, long, and straight hamuli with inclined roots, the lingulate ventral bar membrane, a short marginal sickle with a blunt marginal hook toe of marginal hooks, and an oval male copulatory organ (MCO). <i>Gyrodactylus nigeri</i> n. sp. is the first <i>Gyrodactylus</i> species isolated from <i>Y. niger.</i> Furthermore, phylogenetic analyses showed that the new species is a new member of the subgenus <i>G.</i> (<i>Limnonephrotus</i>).