Gobioecetes longibasais n. sp. (Monogenea: Dactylogyridae) from Rhinogobius similis Gill (Perciformes: Gobiidae) from Okinawa-jima Island, the Ryukyu Archipelago, southern Japan, with a new host record for Gobioecetes biwaensis Ogawa & Itoh, 2017.

Gobioecetes longibasis n. sp. (Monogenea: Dactylogyridae) from the gills of the freshwater goby Rhinogobius similis Gill (Perciformes: Gobiidae) in the River Teima, Okinawa-jima Island, the Ryukyu Archipelago, southern Japan, is described. The new species is distinguished from two congeneric species of Gobioecetes Ogawa & Itoh, 2017, G. rhinogobius (Ling, 1973) and G. biwaensis Ogawa & Itoh, 2017, by having longer ventral hamuli, longer and wider internal process of the dorsal hamuli, and the ratio of dorsal hamulus length to base length. This new species is host-specific to R. similis and considered to be endemic to Okinawa-jima Island or the Ryukyu Archipelago. We also report Rhinogobius sp. OM from a tributary of Lake Biwa, Shiga Prefecture, central Japan, as a new host of G. biwaensis.