Rediscovered historical lots uncover the identity of Nikolaj A. Livanow's Protoclepsis species and clarify the taxonomy of Palearctic waterfowl-associated leeches (Hirudinea: Glossiphoniidae).

In 1902, Nikolaj Livanow described a new genus, Protoclepsis, together with three new nominal species: P. meyeri, P. garjaewi, and P. tessellatoides. The syntypes of the first species were collected in Kazan (European Russia), while those of the two latter species were obtained from Lake Baikal (Siberia). The genus Protoclepsis Livanow, 1902 was established for a group of waterfowl-associated leeches with four pairs of eyespots and represents a synonym of Theromyzon Philippi, 1867. In contrast, the taxonomic concept of Livanow's nominal species was a matter of over a century-long discussion. Here, we revise the taxonomic position of these taxa based upon morphological examination of the original type series that were rediscovered in the Edward Eversman Zoology Museum and Herbarium, Kazan (Volga Region) Federal University, Russia. The lectotype is designated for each of the three nominal species. We found that Protoclepsis garjaewi morphologically corresponds to Hyperboreomyzon polaris Bolotov et al., 2022, although the first taxon was incorrectly described by Livanow as having four pairs of eyespots. Hence, Hyperboreomyzon garjaewi (Livanow, 1902) comb. nov. is proposed. Protoclepsis meyeri represents a synonym of Theromyzon maculosum (Rathke, 1862), as suggested by Livanow himself, while Protoclepsis tessellatoides is a synonym of Theromyzon mollissimum (Grube, 1871). Protoclepsis mollissima Livanow, 1902 incertae sedis has strongly reduced papillation and pigmentation and is tentatively considered a deep-water ecological race of Theromyzon mollissimum. A key for reliable morphological identification of the waterfowl-associated glossiphoniid leeches of Northern Eurasia is also presented. Our findings highlight the low level of endemism of glossiphoniid leeches in Lake Baikal.