Morphological and Molecular Studies of Tetracotyle-Type Metacercariae of the Genus Cotylurus Szidat, 1928 (Trematoda) from the Gravel Snail Lithoglyphus naticoides (Gastropoda) and Host Sex Dependent Differences in Infection Rate

The Ponto-Caspian invader, the gravel snail <i>Lithoglyphus naticoides</i> (C. Pfeiffer, 1828), is infected with a diverse community of digenetic trematodes in its colonized range and most often serves as first intermediate host. We have performed the parasitological examination of <i>L. naticoides</i> snails sampled in Kaunas water reservoir (Lithuania) and found yet unknown strigeid metacercariae of the tetracotyle type using these snails as second intermediate host. In this study, we report data on morphology and molecular analysis based on two markers, the partial 28S rDNA gene and the ITS2 region of these metacercariae. Based on the comparative molecular and phylogenetic analysis, the metacercaria detected in <i>L. naticoides</i> was identified as <i>Cotylurus cornutus</i> (Rudolphi 1809) Szidat, 1928. Differences in metacercariae infection between snail sexes were assessed. The prevalence of infection in <i>L. naticoides</i> was significantly higher in males than in females. Additional molecular markers of tetracotyle of <i>C. cornutus</i> from <i>Stagnicola palustris</i> (O. F. Müller, 1774) and furcocercaria of <i>Cotylurus strigeoides</i> Dubois, 1958 from <i>Physa fontinalis</i> (Linnaeus, 1758), sampled in Curonian Lagoon, Lithuania, were obtained for the first time and used for comparative phylogenetic analysis.