Phylogeny and morphology of some European cyathocotylid digeneans (Trematoda: Diplostomoidea).

The Cyathocotylidae Mühling, 1898 is a family of primitive diplostomoid trematodes important for understanding the evolution of the superfamily Diplostomoidea. However, cyathocotylids remain poorly studied with the use of molecular techniques. In this study we sequenced the 5.8S + ITS2 region, , and genes of two cyathocotylid species and obtained new morphological data on them. We propose nom. nov. instead of the preoccupied name Szidat, 1936 (junior homonym of Stremme, 1911). Adults of cf. (Ishii, 1935) and Katsurada, 1914 were collected from fish-eating birds in the south of the European part of Russia. cf. was very similar to but differed from it in the shape of the testes. The gene dataset provided the best-resolved phylogeny of the Cyathocotylidae to date. In the phylogram based on partial sequences of this gene, was close to members of Dubois, 1983, Chandler & Rausch, 1947 and Szidat, 1936. cf. clustered with members of Mühling, 1896 and Szidat, 1936. Phylogenetic analysis based on the 5.8S + ITS2 dataset showed that adults of examined in our study were conspecific with the metacercariae from the musculature of fish collected in Hungary and Italy. It also revealed probable misidentifications of larvae and adults of cyathocotylids whose sequences are deposited in GenBank NCBI.