Diversity of the Piscicola Species (Hirudinea, Piscicolidae) in the Eastern Palaearctic with a Description of Three New Species and Notes on Their Biogeography

Biodiversity is considered one of the most significant parameters for characterizing aquatic environments. The value of species diversity is taken into account when assessing the ecological state and quality of the ecosystem. However, erroneous taxonomic identification distorts biodiversity signification and, consequently, prevents a clear understanding of ecological signals and traits. In this study, we presented the first data on Piscicola leech species diversity in the vast area of the Eastern Palaearctic. To avoid misidentifications, an integrated approach was applied, combining modern DNA-based and classical morphological methods. Previously, only one species of the genus, Piscicola geometra, was recorded in the whole of Siberia. We discovered three new species: Piscicola sibirica sp. nov., Piscicola khubsugulensis sp. nov. (Eastern Siberia) and Piscicola nordica sp. nov. (European Northeast). The species Piscicola pojmanskae was reduced to synonymy with Piscicola geometra, whose description was updated. Taxonomic adjustments allowed us to ascertain the eastern edge of the Piscicola geometra distribution and to understand the biogeography of the group as a whole. The Piscicola geometra range is limited to Western Siberia, while the widespread Piscicola sibirica sp. nov. and the purely Khovsgolian Piscicola khubsugulensis sp. nov. inhabit Eastern Siberia.