J Zool Syst Evol Res. 2020;00:1–10. wileyonlinelibrary.com/journal/jzs | 1 © 2020 Blackwell Verlag GmbH 1 | INTRODUCTION Our knowledge of the global fauna is continuously enriched with descriptions of new taxa. Over the past 10 years, the species list of the family Glossiphoniidae (flat leeches) increased from 208 (Sket & Trontelj, 2008) to 220 (Beresic-Perrins, Govedich, Banister, & Shuster, 2017; Fedorova & Kaygorodova, 2016; Grosser, Pešić, Berlajolli, & Gligorović, 2016; Iwama, Nogueira, & Gonsalves, 2017; Received: 2 July 2019 | Revised: 3 March 2020 | Accepted: 12 March 2020 DOI: 10.1111/jzs.12385 SHORT COMMUNICATION Species delimitation through DNA barcoding of freshwater leeches of the Glossiphonia genus (Hirudinea: Glossiphoniidae) from Eastern Siberia, Russia Irina Kaygorodova 1 | Nadezhda Bolbat 1,2 | Alexander Bolbat 1 Contributing authors: Nadezhda Bolbat (mandzyak@lin.irk.ru), Alexander Bolbat (bolbatav@lin.irk.ru). 1 Limnological Institute of Siberian Branch of Russian Academy of Sciences, Irkutsk, Russia 2 Department of Plant Physiology, Cell Biology and Genetics, Irkutsk State University, Irkutsk, Russia Correspondence Irina Kaygorodova, Limnological Institute of Siberian Branch of Russian Academy of Sciences, 3 Ulan-Batorskaya st., Irkutsk 664033, Russia. Email: irina@lin.irk.ru Funding information Russian state assignment, Grant/ Award Number: 0345-2019-0002 (AAAA-A20-116122110066-1); Russian Foundation for Basic Research, Grant/Award Number: 17-29-05097 Abstract The study of biodiversity is a priority task of biological science. The structural unit of biodiversity is a species that has a clear identification in a taxonomic system. Morphological features are traditionally the main criteria for species discrimination in zoological studies. However, the presence of inter- and intraspecific polymorphism and phenotypic plasticity makes it difficult to identify species in many groups of in- vertebrates. To solve this problem, in this research, we analyzed morphological and genetic data in combination to delimit species among the Eastern Siberia Glossiphonia leeches using different approaches. Morphology analysis revealed phenetically dis- tinct groups, suggesting the existence of at least two species in the region, G. ver- rucata, a rare Palaearctic species, and a potentially new species Glossiphonia sp. Moreover, sequence-based species delimitation methods congruently supported eight distinct species groups (including two Siberian species) within the available molecular dataset of the Glossiphonia world fauna, using phylogenetic (ML and BI), coalescent (ABGD and GMYC) methods, and pairwise analysis of sequences. The de- tected p-distances (modal value of 0.11) between these 8 groups and the level of genetic polymorphism (max. 0.0041) within groups indicate that the groups are 8 independent species according to the DNA barcoding. Our results once again proved the usefulness of molecular systematics. At the same time, we detected several inac- curacies in the leech species identification, as well as many ambiguous sites in se- quences uploaded on GenBank, which affects the analysis and impedes progress of DNA barcoding technology. KEYWORDS Eastern Siberia, genetic distances, Glossiphonia, molecular taxonomy, species delimitation