New Species of Monopisthocotyla from the gills of Metynnis luna (Characiformes: Serrasalmidae) collected in the Peruvian Amazonia.

Monopisthocotyls represent one of the most diverse groups of ectoparasites associated with Neotropical freshwater fishes; however, their diversity in the Peruvian Amazon remains poorly known. The present study aimed to describe new species of monopisthocotyls parasitizing the gills of Metynnis luna Cope collected in the Nanay River, Loreto, Peru. Twenty specimens of M. luna were examined, from which five new species of monopisthocotyls belonging to the family Dactylogyridae were recovered: four species of the genus Anacanthorus Mizelle & Price, 1965 and one species of Notozothecium Boeger & Kritsky, 1988. Specimens were fixed in 96% ethanol, cleared in Hoyer's medium, and analyzed using phase-contrast microscopy. Taxonomic descriptions were primarily based on the sclerotized structures of the male copulatory organ and the haptor. The results allowed description of Anacanthorus nanayensis n. sp., characterized by a J-shaped tubular cirrus, a short accessory piece, and hooks with an expanded pinhead-like base; A. nanayoides n. sp., distinguished by a simple accessory piece reaching approximately half the length of the cirrus and hooks composed of two subunits; A. ramulus n. sp., characterized by a branch-shaped accessory piece with a conspicuous median projection, slightly undulated cirrus margins, and relatively robust hooks; A. iquitensis n. sp., distinguished by a thick accessory piece with a conspicuous median projection and a length corresponding to approximately three-quarters of the cirrus length; and Notozothecium iquitense n. sp., characterized by an accessory piece basally articulated to the cirrus, composed of two subunits, and dorsal anchors with short, rounded deep roots. These findings expand the current knowledge of dactylogyrid diversity associated with Amazonian serrasalmids and highlight the high, yet still undocumented, parasitic diversity occurring in fishes from the Peruvian Amazonia. Furthermore, this study represents the first record of species of Anacanthorus and Notozothecium parasitizing M. luna.