A new species ofAmeloblastellaKritsky, Mendoza-Franco & Scholz, 2000 (Monogenoidea: Dactylogyridae) from South American freshwater catfishes (Siluriformes: Pimelodidae)

Ameloblastella martinaen. sp. is described from the gills of the pimelodid catfishes (Siluriformes: Pimelodidae)Sorubim lima(Bloch & Schneider) (type-host) andHemisorubim platyrhynchos(Valenciennes) in the Peruvian Amazonia, and onPseudoplatystoma corruscans(Spix & Agassiz) andP. recticulatumEigenmann & Eigenmann in Argentina. The new species is distinguished from other congeners mainly by the morphology of the male copulatory organ (MCO), which has a form of a corkscrew with tight rings, whereas in other species ofAmeloblastellaKritsky, Mendoza-Franco & Scholz, 2000, the MCO is formed by a delicate and coiled tube forming loose rings. Sclerotised structures (haptoral elements and MCO) of specimens ofA. martinaen. sp. were used to compare two parasite populations (from Peru and Argentina) using Euclidean distances. Despite the geographical isolation and different host-associations, both populations belong to the same species. The phylogenetic position ofA. martinaen. sp. was analysed using partial sequences of the 28S rDNA gene along with 46 species of dactylogyrid parasites of siluriforms (Siluriformes) under Maximum Likelihood (ML) and Bayesian Inference (BI) criteria. Phylogenetic reconstructions showed thatAmeloblastellarepresented by five species, including its type-speciesA. chavarriai(Price, 1936) from the heptapteridRhamdia guatemalensisandA. martinaen. sp., was recovered as a well-supported monophyletic group (in both analyses, ML and BI). An additional species,Ameloblastellasp., was found onP. corruscansandP. reticulatumin Argentina. The morphology of the MCO and haptoral elements suggests thatAmeloblastellasp. may represent a new species. However, the few specimens found and the lack of genetic sequences of this species precluded its formal description.