Analysis of zoogeographic, paleogeographic, and molecular data has shown that the ancestors of many fresh-and brackish-water cold-tolerant hydrobionts of the Mediterranean region and the Danube River basin likely originated in East Asia or Central Asia. The fish genera Gasteros-teus, Hucho, Oxynoemacheilus, Salmo, and Schizothorax are examples of these groups among verte-brates, and the genera Magnibursatus (Trematoda), Margaritifera, Potomida, Microcondylaea, Legu-minaia, Unio (Mollusca), and Phagocata (Planaria), among invertebrates. There is reason to believe that their ancestors spread to Europe through the Paratethys (or the proto-Paratethys basin that preceded it), where intense speciation took place and new genera of aquatic organisms arose. Some of the forms that originated in the Paratethys colonized the Mediterranean, and overwhelming data indicate that representatives of the genera Salmo, Caspiomyzon, and Ecrobia migrated during the Miocene from the region of the modern Caspian through the Araks Strait, which existed at that time. From the Ponto-Caspian and the Mediterranean regions, noble salmon, three-spined stickleback, European pearl mussel, seals, and mollusks of the genus Ecrobia spread to the Atlantic Ocean and colonized the Subarctic and Arctic regions of Europe and North America. Our study indicates that the area of the former Paratethys retains its significance as a center of origin of new species and genera and that it has been the starting point of migration “corridors” up to the present time.