Potamotrygonocotyle tsalickisi, new genus and species (Monogenea: Monocotylidae) and Paraheteronchocotyle amazonensis, new genus and species (Monogenea: Hexabothriidae) from Potamotrygon circularis Garman (Chondrichthyes: Potamotrygonidae) in northwestern Brazil. Proceedings of the Biological Society of Washington, 94, 1205–1210
