First morphological and phylogenetic data on (Platyhelminthes: Monogenea) from the Black Sea and the Sea of Japan and molecular evidence of deep divergence of sympatric species parasitizing .

(Gusev, ) Gusev, was collected from the so-iuy mullet (Temminck & Schlegel, 1845) from the Black Sea and the Sea of Japan. DNA sequences data for , as well as its morphological characters from the Sea of Japan were obtained for the first time. Significant morphometric and genetic diversity between specimens of from the Black-Azov Sea region and the Sea of Japan were not found. For the first time, the molecular phylogeny of based on three fragments of the nuclear DNA ribosomal cluster (18S, internal transcribed spacer 1 and 28S) was reconstructed. Molecular analysis of species from the Atlantic and Pacific Oceans revealed a significant phylogenetic distance between and two others species ( and ) from the same host () and region. This result indicates the lack of correspondence between the phylogenetic and geographical closeness of the hosts and the relation of their parasites from the genus .