Dactylogyrids (Platyhelminthes: Monogenoidea) from the gills of Hassar gabiru and Hassar orestis (Siluriformes: Doradidae) from the Xingu Basin, Brazil

Four species of Cosmetocleithrum (three new) and one new species of Vancleaveus are described or reported parasitizing the gills of doradid catfishes (Siluriformes) from Xingu River and related tributaries: Cosmetocleithrum phryctophallus sp. nov. and Cosmetocleithrum bifurcum Mendoza-Franco, Mendoza-Palmero & Scholz, 2016 from Hassar orestis; Cosmetocleithrum leandroi sp. nov. from Hassar gabiru; Cosmetocleithrum akuanduba sp. nov. and Vancleaveus klasseni sp. nov. from Hassar orestis and H. gabiru. Cosmetocleithrum phryctophallus sp. nov. differs from its congeners by possessing a male copulatory organ (MCO) with 2 ½ counterclockwise rings, and an accessory piece with an elongate torch-shaped blade. Cosmetocleithrum leandroi sp. nov. has a MCO comprising a coil of about 3 ½ rings, a sigmoid accessory piece with a cup-shaped distal portion, a single type of hooks, and anchors with poorly differentiated roots. Cosmetocleithrum akuanduba sp. nov. is characterized mainly by having a J-shaped MCO, an elongate accessory piece with sharp distal region, distal portion with a small gutter, and a heavily sclerotized vagina with short “S”-shaped vaginal canal. Vancleaveus klasseni sp. nov. differs from the other species of the genus occurring in doradids by possessing anchors with triangular to subtriangular superficial root, developed deep root, and a coiled MCO with 2 ½ counterclockwise rings. Cosmetocleithrum bifurcum was reported for the first time parasitizing doradids from Brazilian Amazon.