Abstract: In numerous aspects Lake Baikal is the world most splendid lake of the whole world, just to mention, it is the deepest lake and contains the worlds largest volume of surface freshwater. Located in the so called Baikal Lake rift zone the basin is filled with the thick sedimentary sequence. The origin of the rift zone began over 30 million years BP in the Oligocene. Baikal represents a group of ancient lakes which extends back with their geological history to the Tertiary. Examples of such lakes include also Biva in Japan and Ohrid in Macedonia, East African rift valley lakes including Lake Victoria, Tanganyika and Titicaca in South America. Ancient lakes attract the attention of evolutionists and taxonomists as water bodies hosting a wealth of interesting plant and animals species. It has already been observed in the early years of studies on plant and animals communities and on diatom assemblages in particular that taxa at different rank are restricted in their distribution (endemic) either to ancient lakes themselves or to their close surrounding area. In the forwarded monograph we provide description and illustrate in LM and SEM numerous diatoms. Most significant achievement of our study is that we describe as new for science over 200 species and illustrate over 170 entities which potentially are new for science. It is noteworthy that in this monograph we describe and illustrated taxa representing just 27 genera. In this book we present the highlights of benthic pennate diatom taxa which inhabit just a small piece of the Lake Baikal surface bottom sediments. The major aim of this monograph is to document the biodiversity of the Lake Baikal diatom assemblages. The Lake has turned out to be so rich in species number that we can easily plan the next volume only just to provide the diatomologists with the diversity of the Lake Baikal pennate diatoms and the samples accessible for our examination are just like a tip of the needle when compared to the study area size. The most remarkable observation is that, although Lake Baikal is an ancient lake located in Siberia, a part of the Holarctic, the species composition of its benthic diatom assemblages is fairly different from any other regions of this realm. Without any doubt our research on diatom assemblages supports the hypothesis of Lake Baikal being an evolutionary hotspot. Numerous diatom genera which neither on European nor on the global scale never reach such diversity as it is observed in the Baikal. Results of our study support a hypothesis that diatom assemblages of the Baikal Diatom shallow areas are composed of numerous taxa, either common or rare, which have much broader distributed in the Holarctic realm being. Apparently less numerous are taxa considered as Baikal endemics. Surprisingly the species of the deep water appear to be endemic form. They are almost entirely missing even in neighboring regions including northern Mongolia (Lake Hövsgöl), as documented in our own research.weiterlesen