Diversity of European lissorchiid trematodes from fish and snail hosts with comments on the validity of the genus Szidat, 1943.

Genetic markers, DNA sequences and karyotypes, of some European lissorchiid species from their intermediate and final hosts were obtained to clarify controversial data about their life cycles and taxonomy, and to reveal phylogenetic affinities. The life cycles of three species have been confirmed for the first time based on molecular data. Comparative analysis of internal transcribed spacer 2 (ITS2) and partial 28S rDNA sequences has undoubtedly proven that cercariaeum of type-species of the genus , , develops in pulmonate snails, and , but not in the genus . The faucet snail, , serves as the first intermediate host for (=) and ; adults of both species were isolated from the common rudd, . It has also been confirmed that serves as the second intermediate host for . Phylogenetic analysis supports the validity of the genus . Two species, and , with cercariaeum belonging to the group, are closely related and are being recovered as a well-defined evolutionary lineage in phylogenetic trees. A significant divergence between spp. and spp. was revealed. The diploid chromosome set of is composed of 14 chromosomes and does not show similarities with karyotypes of other lissorchiid species. and share the basal diploid value of the family, 2n = 20, and reveal very close morphology of the corresponding chromosome pairs. Karyotypic similarities of these species are in accordance with molecular phylogenetic data. Thus, the available molecular and cytogenetic data support the assignment of and to a separate genus, meanwhile, the assignment of to the genus was not justified.