Morphology and molecular characterisation of two new species of Mymarothecioides (Monopisthocotyla: Dactylogyridae) parasitising the gills of anostomid fishes from Brazil.

Using an integrative taxonomic approach, we describe two new species of Monopisthocotyla, Mymarothecioides leporini n. sp. and Mymarothecioides paranaensis n. sp., parasitising the gills of anostomid fishes from the Jaguaribe River and Paraná River basins, Brazil. These descriptions represent the first record of species of Mymarothecioides in hosts of the family Anostomidae. Mymarothecioides leporini n. sp. is distinguished by a male copulatory organ (MCO) with a spoon-shaped distal portion and a ventral bar with an ornamented anteromedial process. Mymarothecioides paranaensis n. sp. differs from its congeners by possessing a sclerotised, arcuate MCO with a rounded tip and a rectangular-shaped basal flap. Molecular analyses of Large Subunit ribosomal DNA (LSU rDNA) and Mitochondrial Region of Cytochrome C Oxidase subunit 1 (COI mtDNA) markers support the validity of both taxa, placing them as distinct molecular operational taxonomic units (MOTUs). High genetic distances (17.8%-18.7% for COI) confirmed the separation between the two new species. Additionally, this study provides the first molecular characterisation for the genus. These findings expand the known geographical distribution and host range of Mymarothecioides, contributing to the knowledge of dactylogyrid diversity in Neotropical freshwater systems.