Integrative Taxonomy of Tereancistrum spp. (Monopisthocotyla: Dactylogyridae) Parasites of the Gills of Freshwater Fishes from the Caatinga Domain, Brazil

<i>Tereancistrum</i> is a common genus of Neotropical monopisthocotylans; however, information on its diversity and phylogeny remains limited. In this study, we describe four new species of <i>Tereancistrum</i> parasitizing the gills of <i>Prochilodus brevis</i> (Characiformes: Prochilodontidae) from a weir in the state of Ceará, Brazil. <i>Tereancistrum spiralocirrum</i> n. sp. and <i>Tereancistrum scleritelongatum</i> n. sp. are characterized by a dextro-ventral vaginal pore and a Y-shaped dorsal bar. Notably, <i>Tereancistrum spiralocirrum</i> n. sp. is the first species in the genus to possess a male copulatory organ (MCO) with multiple rings (16 to 18). In contrast, <i>Tereancistrum ancistrum</i> n. sp. and <i>Tereancistrum kritskyi</i> n. sp. are distinguished by a sinistral vaginal pore, a sclerotized MCO in the form of a coiled tube with slightly more than one clockwise ring, and an accessory piece that is non-articulated with the base of the MCO. However, <i>Tereancistrum ancistrum</i> n. sp. is unique in lacking a dorsal bar. Sequences of the LSU rDNA obtained from seven species of <i>Tereancistrum</i> parasitizing <i>P. brevis</i> and <i>Leporinus piau</i>, along with published sequences of other Dactylogyridae members, were included in the molecular analyses. Phylogenetic reconstructions supported the monophyly of <i>Tereancistrum</i>.