Based on morphological and molecular studies, including analysis of variation of four molecular markers, there are two orientocreadiid species, Orientocreadium cf. pseudobagri and O. cf. elegans, in the south of the Russian Far East. Trematodes of these two species possess morphological and molecular variation that is most possibly related to population formation processes for these species in the investigated territory. Our molecular data show that the trematode assemblages studied were subdivided for 28S rDNA markers into two large groups related to basins in different water bodies. Nucleotide sequences of these groups are closely related to each other. Within each group there are specific nucleotide substitutions that are unique for several geographical local samples of trematodes. This variation reflects local processes of divergence of these worms. Results of the median-joining network analysis based on concatenated mitochondrial cox1 and nd1 gene sequences support this inference, showing the existence of four groups of haplotypes of Orientocreadium trematodes that are associated with geographical locations.
