Dactylogyridae (Monopisthocotyla) parasitizing Caenotropus labyrinthicus (Characiformes: Chilodontidae) from the Tocantins and Gurupi river basins, northern Brazil, with the proposal of Tocantinsiella n. gen. (Dactylogyridae) and four new species

Four new species, assigned to the proposed new genus Tocantinsiella n. gen., were described from the gills of Caenotropus labyrinthicus collected in the Tocantins and Gurupi river basins, northern Brazil: Tocantinsiella maranhensis n. sp., Tocantinsiella brassicae n. sp., Tocantinsiella vesiculosa n. sp., and Tocantinsiella flabellata n. sp. The new species are characterized mainly by the presence of a sclerotized, robust, and sinistral vaginal vestibule, as well as a copulatory ligament connecting the male copulatory organ (MCO) from the accessory piece, which represent morphological and diagnostic characteristics for the proposed new genus. Tocantinsiella n. gen. is morphologically similar to Heterothecium due to the presence of a sclerotized, sinistral vaginal vestibule, differing due to the presence of a copulatory ligament and a non-articulated MCO. Philocorydoras also shares similarities related to the morphology of the copulatory complex. However, species of this genus are recorded only in Siluriformes fishes. This study provides a significant expansion of the diversity of helminth fauna in fishes of the family Chilodontidae by describing a new genus and four new species of Monopisthocotyla in the host studied.