Monopisthocotyla parasites of the gills of Triportheus albus (Characiformes: Triportheidae) from the Itaya River, Peru, including the description of two new species of Anacanthorus Mizelle & Price, 1965.

Fourteen species of monopisthocotyls were reported from the gills of Triportheus albus Cope (Characiformes: Triportheidae) collected from the Itaya River, Peru. Nine species belonged to Anacanthorus Mizelle & Price, 1965: seven previously described species: Anacanthorus acuminatus Kritsky, Boeger & Van Every, 1992, Anacanthorus alatus Kritsky, Boeger & Van Every, 1992, Anacanthorus bellus Kritsky, Boeger & Van Every, 1992, Anacanthorus euryphallus Kritsky, Boeger & Van Every, 1992, Anacanthorus quinqueramus Kritsky, Boeger & Van Every, 1992, Anacanthorus formosus Kritsky, Boeger & Van Every, 1992, and Anacanthorus ramulosus Kritsky, Boeger & Van Every, 1992, and two new species described herein. Three species belonged to Ancistrohaptor Agarwal & Kritsky, 1998: Ancistrohaptor falciferum Agarwal & Kritsky, 1998, Ancistrohaptor falcunculum Agarwal & Kritsky, 1998, and Ancistrohaptor forficata Diniz, de Sousa, Yamada & Yamada, 2025; and two to Jainus Mizelle, Kritsky & Crane, 1968: Jainus iquitensis Morey, Viana, Chota & Chero, 2025 and Jainus sardinae Morey, Viana, Chota & Chero, 2025. Anacanthorus itayensis n. sp. is characterized by a long sclerotized sigmoid male copulatory organ (MCO) with submedial cirral "feather" and by a four-branched accessory piece in which the second branch terminates in a fish-like fin, the others bifurcate into sub-branches with pointed tips. Anacanthorus ypsiloniformis n. sp. is characterized by an elongate, slightly conical MCO curving ventrally and terminating in a rounded, slightly tapered distal tip bearing a dense crown-like cluster with submedial small spines, and by a distinctively Y-shaped accessory piece with two divergent arms arising proximally: one broader and blunt-ended with a comb-like denticulate distal margin, the other narrower and more rounded distally. This study constitutes the first comprehensive record of monopisthocotyls from T. albus in Peru and documents one of the most species-rich dactylogyrid assemblages reported from a single host species of Triportheus Cope in the Neotropical region.