Mudsnails Peringia ulvae serve as hosts for many digenean species; some of them differ a lot in their life cycle pattern. In the north of Europe two contrasting examples are Cryptocotyle concava (Heterophyidae) with a trixenous life cycle and Bunocotyle progenetica (Hemiuridae) with a monoxenous life cycle. A ~ 870 base pairs long fragment of cox1 gene sequence was used to evaluate and compare genetic structure within these two species. Our findings suggest that high dispersal of C. concava keeps differentiation between different locations minimal and haplotype diversity quite high. In B. progenetica two haplotypes dominate and have at least limited dispersal.