The first results of DNA barcoding of freshwater Oligochaeta (Annelida) of the European North-East of Russia

Oligochaetes inhabiting freshwater ecosystems are considered promising indicators of ecological status due to their sensitivity to environmental changes. However, traditional identification based on morphological characteristics is often challenging. The application of molecular techniques, particularly DNA barcoding of the mitochondrial cytochrome c oxidase subunit I (cox1) gene, improves the accuracy of species identification and enhances our understanding of oligochaete genetic diversity. This study presents new data on taxonomic and genetic diversity of aquatic oligochaetes (Annelida, Clitellata) from various freshwater bodies in the European North-East of Russia. A discrepancy was revealed between morphological (17 species) and molecular (26 genetic lineages) differentiation of taxa. Significant cryptic diversity was recorded in Tubifex tubifex (Müller, 1774) and Limnodrilus hoffmeisteri Claparède, 1862, which were subdivided into 11 genetic lineages, with maximum intraspecific cox1 distances reaching up to 26.1%. The presence of Tasserkidrilus kessleri (Hrabě, 1962), identified through molecular data, was recorded for the first time in the Vychegda River basin. The results confirm the high effectiveness of molecular approaches for studying biodiversity in northern freshwater ecosystems and provide a foundation for the development of a regional reference library of DNA barcodes.