An integrative taxonomic approach to the description of a new species of Jainus Mizelle, Kritsky & Crane, 1968 (Monopisthocotyla: Dactylogyridae) parasitizing a triportheid host from Brazil

Abstract

The present study describes a new species of Jainus (Dactylogyridae) parasitizing the gills of Agoniates halecinus Müller & Troschel, 1845 (Triportheidae) from Brazil. The new species differs from its congeners primarily by a unique combination of haptoral and copulatory characters. The ventral anchors possess a short superficial root and an elongate deep root, both bearing long, slender, weakly sclerotized extensions, whereas the ventral bar bears a comparatively long, weakly sclerotized median process. The new species also presents dissimilar hooks and a distinctive copulatory complex, characterized by a J-shaped male copulatory organ (MCO) forming a single counterclockwise ring and an accessory piece connected to the base of the MCO by a delicate ligament. The accessory piece is laminar, with pointed extremities, a distal opening through which the copulatory tube passes, and an elongate, strongly curved projection tapering to a pointed tip. Phylogenetic analyses based on partial large subunit (LSU) rDNA and cytochrome c oxidase subunit I (COI) mtDNA sequences recovered the two sequences of the new species together as a distinct lineage within Jainus. Molecular characterization of the new species provides additional sequence data for the genus and contributes to the current framework for investigating phylogenetic relationships within Jainus. This study represents the first record of a species of Jainus parasitizing a fish of the genus Agoniates , expanding the known host range of Jainus and increasing knowledge of its diversity within Triportheidae. These findings contribute to a broader understanding of the diversity and host associations of monopisthocotylans infecting Neotropical freshwater fishes.