A re-evaluation of conflicting taxonomic structures of Eurasian <i>Triaenophorus</i> spp. (Cestoda, Bothriocephalidea: Triaenophoridae) based on partial <i>cox1</i> mtDNA and 28S rRNA gene sequences

Cestodes of the genus Triaenophorus Rudolphi, 1793 are widely distributed parasites of Esocidae, Percidae, Salmonidae, Thimallidae, Cobitidae, Osmeridae, Cyprinidae, Cottiidae, Lotidae, and several others in the Holarctic. The taxonomic arrangements of different authors, based on morphological and ecological–biogeographic characters, suggest the presence of two to five species of this genus in Eurasia. The genetic variation of Eurasian Triaenophorus spp. was evaluated using DNA barcoding ( cox1 and 28S gene sequences). This confirmed the validity of five Triaenophorus species: T. amurensis, T. crassus, T. meridionalis, T. nodulosus, and T. orientalis. We demonstrated systematic concordance between traditional meristic criteria and DNA sequence data. Phylogenetic reconstructions support the monophyletic origin of the group of species with a long basal plate of the scolex hook ( T. crassus, T. meridionalis, and T. orientalis). Triaenophorus crassus is represented by two haplogroups, associated with Siberia and northwestern Russia. Our results show differences between T. nodulosus, T. amurensis, and T. crassus in terms of the haplotype diversity level, which are probably related to the Quaternary history of the development of their ranges, as well as the degree of euryxeny to the second intermediate host.