Genetic characterization of far eastern species of the genus Crepidostomum (Trematoda: Allocreadiidae) by means of 28S ribosomal DNA sequences

Genetic divergence and phylogenetic relationships of four species of the genus Crepidostomum Braun, 1900 sensu Caira, Bogea (2005) were revealed using partial sequences of 28S ribosomal RNA gene. Genetic divergence between C. cf. farionis (Muller, 1784) and C. nemachilus Krotov, 1959 was 3.1%, which corresponds to the mean value of interspecific divergence between Crepidostomum species. These two species, therefore, can be recognized as bonafide species. However, we found no genetic differences between 28S rRNA gene sequences of C. nemachilus and C. cf. metoecus Braun,1900 inspite of considerable morphological and ecological differences. Maximal values of genetic p-distances were revealed between C. cf. auriculatum Wedl, 1857 and C. cf. farionis. Phylogenetic relationships of Crepidostomum spp. for which sequence data are available, along with species in other related genera (Bunodera Railliet, 1896 and Allocreadium Loss, 1900) showed a paraphyly of the genus Crepidostomum. Considerable differentiation of C. cf. auriculatum from other Crepidostomum species was revealed, which may reflect the original description of this species in a separate genus Acrolichanus Ward, 1917. Our results are consistent with the conventional systematics that places the four genera (Crepidostomum, Bunodera, Megalogonia and Allocreadium) within the same family.