The study of genetic diversity not just between, but also within the species, is important for understanding the ecological and evolutionary trends. In case of the digeneans, one can may expect that intraspecific diversity is largely determined by the characteristics of their life cycles: the host identities, agility, and living environment; reproduction features at different life cycle stages; and other. We for the first time evaluate the intraspecific diversity in digeneans with one-, two- and three-host life cycles that occur in the coasts of the northern seas. The material for the study are the three species: Bunocotyle progenetica Chabaud & Buttner, 1959, Tristriata anatis Belopolskaia, 1953 and Cryptocotyle lingua (Creplin, 1825) Fischoeder, 1903. The major approach is sequencing of the marker DNA fragments (several mitochondrial genes) followed by the haplotype network analysis. The key step of the study was the DNA marker and primer design (previously published primers did not suffice). In the talk we will present the preliminary results of the project.