An Illustrated Checklist of Leech Species from Lake Baikal (Eastern Siberia, Russia)

New data on Lake Baikal fauna of Hirudinida (Annelida, Clitellata) are presented. The species composition of Baikal leeches extends to 20 species belonging to two orders, four families, and 12 genera. An updated checklist includes information on five species recorded in Eastern Siberia for the first time. All specimens from author’s collection are provided with illustration. 1. Introduction Lake Baikal is situated in the northeast of Central Asia. It is one of the most ancient (25–30？MY), the deepest (1637？m), and the largest (volume of 23？000？km3, length of 636？km, width up to 80？km, catchment area of 540？000？km2, and coastline of 1800？km) repository of single volume of unfrozen fresh water of the planet (20% of the global supply) [1]. Transparency of the Baikal water reaches 40–50？m with extremely poor mineralization 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 organisms (1550 animal species and over 1000 species of plants) [2]. Lake Baikal now holds the largest number of described metazoan species of all known lakes and can be considered as a centre of megadiversity. The organisms inhabiting the lake adapted to a variety of environmental conditions, having mastered and repopulating the diversity of habitats from interstitial zone to maximal depths. The pronounced endemism and specific wealth of its fauna (82% of known species) has attached a keen interest of biologists and biogeographers worldwide. A start of Lake Baikal studies occurred at the middle of the eighteenth century, but they have been carried out with the greatest intensity in the twentieth century. Despite a 200-year history of limnological studies, Lake Baikal is still full of white spots; one of them is the fauna of parasitic annelids. 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 [2]. These species are adapted to living in cold, clean, oxygenated water and fed by Baikal endemic animals: bullheads, amphipods, 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 Lake Baikal fauna. 2. Methodology The previously published information and an extensive material collected by the author in the period from 2002