Morphology and molecular phylogeny of Bychowsky & Nagibina, 1969 (Monogenoidea) parasitizing marine catfish (Ariidae) from the Atlantic coast of South America: a new species, supplementary taxonomic information and new insights.

In this study, a new dactylogyrid species is described from the gills of two ariid fish species of the Brazilian coast, and , by combining morphological characters with partial sequences. The new species can be distinguished from its congeners by the following morphological characteristics: a male copulatory organ (MCO), a coiled tubular shaft of around one counterclockwise ring, base with a sclerotized cap; MCO with tapered distal region; a T-shaped accessory piece; a vagina, a cup-shaped vaginal vestibule, slightly sclerotized; and a pharynx comprising a muscular, glandular bulb. Supplementary taxonomic data for from (type-host) are also presented and new sequences of spp. from other ariid fish from South America are provided. Phylogenetic analyses based on partial gene sequences placed n. sp. and as two early divergent lineages within from South America. Finally, a way to test the monophyly of and is also discussed, which may be useful for future studies.