Atopogyrodactylus n. gen. (Gyrodactylidae) is proposed for Atopogyrodactylus praecipuus n. sp. (type species by monotypy), a protandrous and oviparous gyrodactylid from the external surfaces of an unidentified bristlenose catfish Ancistrus sp. (Siluriformes: Loricariidae) from the head waters of the Rio Candeias in the State of Rondônia, Brazil. The new genus contains species morphologically similar to those of Nothogyrodactylus Kritsky Boeger, 1991 as shown by members of both genera having accessory copulatory sclerites associated with the male copulatory organ (MCO). Atopogyrodactylus differs from Nothogyrodactylus by its species lacking haptoral bars and having a sclerotized haptoral plate overlying the ventral anchors. The new species most closely resembles Nothogyrodactylus amazonicus Kritsky Boeger, 1991 by possessing a flared proximal filament on the egg and a single morphologically similar accessory copulatory sclerite associated with an allantoid MCO.
Keywords: Platyhelminthes, Monogenoidea, Gyrodactylidae, oviparous gyrodactylid, Atopogyrodactylus n. gen., Atopogyrodactylus praecipuus n. sp., Loricariidae, bristlenose catfish, Ancistrus sp., Amazon, Brazil.