ORIGIN AND EVOLUTION OF THE FAUNA OF FREE -LIVING TURBELLARIA OF LAKEBAIKAL

A brief survey of hypotheses of the origin of invertebrate fauna of La ke Baikal and their basic characteristics are given. The present state of knowledge of the endemic turbellarian fauna is considered. Problem s of freshwater or marine origin and the age of endemic groups of spec ies, unsimultaneous invasion of ancestral forms, isolation of the ende mic faune from the palaearctic one etc. are considered basing on nativ e turbellarian worms. The given facts show, that Turbellaria are among the most important groups of invertebrates inhabiting the lake. The p resent composition and complicated history of turbellarian fauna in La ke Baikal can be used for illustration and critical consideration of t he problems concerning the origin of unique fauna in this lake.