49 Lauterbornia 75: 49-62, D-86424 Dinkelscherben, 2012-12-03 A revised checklist of the Lake Baikal Hirudinida fauna Irina Kaygorodova With 20 figures Keywords: Hirudinida, Hirudinea, Lake Baikal, Siberia, Russia, distribution, faunistics Schlagwörter: Hirudinida, Hirudinea, Baikalsee, Sibirien, Russland, Verbreitung, Faunistik New data on the Lake Baikal fauna of Hirudinida (Annelida, Clitellata) are presented. The species composition of Baikal leeches extends to 22 species belonging to 2 orders, 4 families and 13 genera. An updated checklist in- cludes information on 2 species recorded in Eastern Siberia for the first time. All specimens from the author’s collection are provided with an illustration of preferably live animals. 1 Introduction Lake Baikal is situated in the north-east of Central Asia. The lake is one of the most ancient (25–30 million years), the deepest (1637 m), the largest (volume of 23 000 km³, length of 636 km, maximal width up to 80 km, catchment area of 540 000 km², coastline of 1 800 km) fresh- water reservoir and is repository of 20 % of unfrozen fresh water of the planet (Kozhova & Izmest’eva 1998). Transparency of the Baikal water reaches 40–50 m. The lake has extremely poor mineraliza- tion and higher oxygen saturation. The oxygen content at the bottom even in the deepest areas is no lower than 70–-80 % of saturation. The combination of these factors, together with numerous other ones, has resulted in the fact that the lake has a unique complex of living or- ganisms. Lake Baikal now holds the largest number of described metazoan species of all known lakes and can be considered as a centre of megadiversity (1550 animal species and over 1000 species of plants) (Timoshkin 2001). The organisms inhabiting the lake adapted to a vari- ety of environmental conditions, having mastered and repopulating the diversity of habitats from interstitial zone to maximal depths. The endemism of its fauna is about 82 % of known species. A start of Lake Baikal scientific studies occurred at the middle of the 18th century, but they have been carried out with the greatest intensity in the 20th century. Despite a long period of studying, Lake Baikal is still full of "white spots", one of them is the fauna of para- sitic Annelida. Baikal leeches demonstrate a high level of biological diversity and endemism, both at the genus level and at the species level. By 2001, there were 13 leech species stated in Lake Baikal (Timoshkin 2001). Recently this species list was extended to 20 species (Kaygorodova 2012). All Baikal species are adapted to living in cold, clean, oxygenated water and fed by Baikal en- demic animals: fishes, Amphipoda, Mollusca, and perhaps other groups. Unfortunately, there is still no clear idea on their preferences to a host. The aim of this paper is to update knowledge on leech species composition of the Lake Baikal fauna. 2 Material and methods References data and an extensive material collected by the author in the period from 2002 to 2012 were used in this paper. Species definition was done with identification keys (Lukin 1976, Epstein 1987, Nesemann & Neubert 1999) and the original descriptions (Lukin & Epshtein