The phylogenetic position of the unusual diplostomoidean genus Schwartzitrema Vigueras, 1941 (Digenea, Diplostomoidea) and description of 2 new species from Neotropics.

Schwartzitrema Vigueras, 1941, is a small, rarely reported genus of diplostomoideans that parasitize avian definitive hosts, predominantly anhingas, on several continents. No DNA sequences were previously available for any Schwartzitrema spp. In the present study, we describe adults of 2 new Schwartzitrema spp. from anhingas in Brazil. We also provide description of metacercaria of one of the new species from Argentina. Schwartzitrema macrotesticulata n. sp. lacks a clear separation between its testes, appearing almost as a contiguous, irregularly shaped, lobular mass. A highly characteristic feature of Schwartzitrema macroholdfastus n. sp. is a strongly enlarged lobe of the holdfast organ. These features, along with distribution of vitellarium and nature of the preputial folds surrounding the genital cones, separate the new species from their congeners. We generated partial sequences of the large ribosomal subunit (28S) rDNA and cytochrome c oxidase subunit I (cox1) mtDNA genes from adult forms of both species and cox1 of metacercarial stages. The 28S sequences were used for phylogenetic inference. The pairwise sequence divergence between the 2 species is 4.0-4.6% in cox1 gene. Intraspecific variability in the same cox1 region did not exceed 0.8% despite the long geographic distance between collecting sites in Brazil and Argentina.