The present study describes three new species of monogeneans parasitizing the gills of anostomid fishes from the Upper Paraná River basin, southeastern Brazil: Jainus beccus n. sp. and Jainus radixelongatus n. sp. on Leporinus friderici, Leporinus octofasciatus, Leporinus striatus, and Megaleporinus elongatus; and Jainus ornatus n. sp. on L. friderici. The new species differ from other congeners by the morphology of the accessory piece. There is a semicircular distal portion resembling a “bird’s beak” in Jainus beccus n. sp. It composed of two subunits—one ventral and more sclerotized, sickle-shaped, and another dorsal with three projections—in Jainus radixelongatus n. sp. There are two elongated and sclerotized subunits, both of which have a sickle-shaped distal portion, in Jainus ornatus n. sp. Supplementary observations not reported in the original descriptions of the type-species Jainus piava Karling, Bellay, Takemoto & Pavanelli, 2011 are proposed, as follows: the presence of a thin and delicate ventral bar, which can vary greatly in shape; an accessory piece not articulated with the MCO’s base. This paper provides the first phylogenetic study based on LSU rDNA and COI mtDNA gene sequences for Jainus, improving and clarifying the understanding of host–parasite relationships in neotropical characiforms.

The present study describes two new species of monopisthocotylans parasitizing the gills of Cyphocharax modestus (Characiformes: Curimatidae) from two localities of the Upper Paraná River basin, state of São Paulo, Brazil. Urocleidoides saghirus n. sp. and Urocleidoides taquariensis n. sp. differ from other congeners mainly in the morphology of the accessory piece: comprising two subunits (one scythe-shaped subunit, and one adjacent piece with a narrow base broadening towards the upper end, which is axe-shaped) in Urocleidoides saghirus n. sp., and a straight rod with a bifurcated proximal portion, a distal portion ending in a point, and two curved handles arising from the medial portion and uniting close to the distal portion in Urocleidoides taquariensis n. sp. The phylogenetic analyses revealed Urocleidoides to be non-monophyletic, indicating the need for a taxonomic review. This study provides the first molecular sequences for Urocleidoides spp. parasitizing Curimatidae, including the newly described species. These findings revealed distinct clades and suggested possible host specificity, underscoring the importance of additional research to better understand the phylogenetic relationships within the genus.

Diversity of Creptotrema was investigated using morphological and molecular tools, including data for Creptotrema creptotrema (type-species). Three new species, parasites of Brazilian fishes, are described: Creptotrema conconae n. sp. (type-host, Imparfinis mirini Haseman), Creptotrema schubarti n. sp. (type-host, Characidium schubarti Travassos) and Creptotrema megacetabularis n. sp. (type-host, Auchenipterus osteomystax (Miranda Ribeiro)). The diagnosis of the genus was amended to include new features. The new species differ from each other mainly in terms of body shape, relative sucker size, and testes position. DNA sequences were obtained from Creptotrema spp. from Brazil, including 28S, ITS and COI. Genetic divergences among the new species and C. creptotrema varied from 2.1 to 5.2% (21–49 bp) for 28S, and 6.6 to 16.4% (21–45 bp) for COI. Phylogenetic analysis (28S) placed the newly generated DNA sequences of Creptotrema in a clade (Creptotrema clade sensu stricto) composed of C. creptotrema, the new species described herein, and all species previously described as Auriculostoma, revealing that Auriculostoma is best interpreted as a synonym of Creptotrema based on the principle of priority of zoological nomenclature. Creptotrema funduli, the single sequence of the genus previously available, was not grouped within the Creptotrema clade sensu stricto, suggesting the need for reevaluation of the taxonomic status of this species. Our results showed that Creptotrema represents a monophyletic genus of trematodes widely distributed across the Americas, which currently comprises 19 valid species of parasites of teleosts and anurans.

The present study describes a new species of Cosmetocleithrum Kritsky, Thatcher and Boeger, 1986 from the gills of the catfish Trachelyopterus galeatus (Linnaeus, 1766) from the mouth of the Aguapeí River, municipality of Castilho, São Paulo State, Brazil. Cosmetocleithrum laciniatum n. sp. closely resembles Cosmetocleithrum striatuli Abdallah, Azevedo and Luque, 2012 and Cosmetocleithrum longivaginatum Suriano and Incorvaia, 1995 by the shape of dorsal and ventral bars (straight with enlarged ends), and Cosmetocleithrum gussevi Kritsky, Thatcher and Boeger, 1986 by having a Y-shaped accessory piece. The new species can be distinguished from most of its congeners by having a coiled cirrus with a 1½ counterclockwise ring with a sclerotized base possessing lateral flaps. This species is the second found to contain members of Cosmetocleithrum parasitizing the gills of Auchenipteridae. A note on the morphology of C. striatuli, a parasite of Trachelyopterus striatulus, is also presented.