A high-altitude population of Hyperboreomyzon polaris (Hirudinea: Glossiphoniidae) in Altai Mountains, South Siberia, Russia.

Hyperboreomyzon polaris Bolotov, Eliseeva, Klass & Kondakov, 2022 (Hirudinea: Glossiphoniidae) is an enigmatic freshwater leech that was recently described based on three specimens from two remote regions of the Eurasian Arctic, that is, the Kolguev Island and Putorana Plateau, Russia. Later on, misidentified historical samples of this species were discovered in the Hirudinea collection of Zoological Institute of the Russian Academy of Sciences (St. Petersburg, Russia). These samples were collected by Pavel G. Ignatov, a prominent Russian geographer and traveler, from a remote high-altitude area of the Altai Mountains (South Siberia) in 1901. To collect new samples from this population, we organized a field expedition to the same area (Lake Dzhulukul) in 2023. Molecular genetic data (COI and 18S rRNA) obtained from newly collected specimens revealed that they belong to H. polaris. Hence, this leech could be considered an Arctic-alpine species, the disjunctive range of which covers Arctic areas of Eurasia and Central Asian (South Siberian) mountains. We describe and illustrate living individuals of H. polaris for the first time, update its morphological diagnosis, present a life cycle reconstruction based on the frequency of four size classes in available samples. It is shown that this species prefers small lentic water bodies such as small lakes and lakelets. The crop content of a well-fed specimen from Altai contains DNA of the northern pintail Anas acuta Linnaeus (Aves: Anatidae), indicating that H. polaris feeds on blood of waterfowl. Our results indicate that Hyperboreomyzon may be considered a species adapted to cold high-latitude areas and mountain refugia.