New insights in the systematics of the Hemiuroidea (Digenea: Hemiurata) based on the integrative taxonomy approach.

Opistholecithum sandugaense n. g. n. sp. was collected from the intestine of Oncorhynchus keta (Walbaum) in the Nezhinka (=Sanduga) River, Primorsky region, Russia. Based on the position of the vitellarium in hindbody and significant genetic differentiation, ten species from the genus Lecithaster Lühe, 1901 were transferred to the newly established Opistholecithum as follows: O. gibbosum (Rudolphi, 1802) n. comb., O. macrocotyle (Szidat & Graefe, 1967) n. comb., O. micropsi (Zdzitowiecki, 1992) n. comb., O. salmonis (Yamaguti, 1934) n. comb. According to the morphometrics and topology of the internal organs, O. sandugaense appears similar to O. salmonis. These species are distinct based on novel sequence data - 28S rRNA gene (p-distances 0.4%) and the cox1 mtDNA gene (p-distances 4.4-4.8%). Large-scale phylogeny reconstruction showed that the lecithasterid subfamily Lecithasterinae sensu stricto include two genera Lecithaster (type taxon) and Opistholecithum n. g.; other genera Lecithophyllum and Aponurus were transferred to the family Lecithophyllidae n. stat. Based on the morphological features, we consider four subfamilies Lecithasterinae, Trifoliovariinae, Prolecithinae and Macradenininae belonging to Lecithasteridae. Analysis of indels in the 28S divergent domains proved to be a robust technic for family delimitation within the superfamily Hemiuroidea. Especially it allows to reveal the molecular symplesiomorphies affecting phylogenetic reconstructions. Taxonomic rearrangements proposed in this study are supplemented by dichotomous keys: (1) for two genera of the subfamily Lecithasterinae; (2) for the genus Opistholecithum; (3) for the genus Lecithaster; (4) for six closely related hemiuroid families, with Lecithophyllidae n. stat. (genera Lecithophyllum, Aponurus, Monorchiaponurus, Weketrema) and Merlucciotrematidae n. fam. (Merlucciotrema).