582 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



(except for the passive immigrant Dreissena polymorpha) and of polychaetes 

 underlines the importance of a capability for active migration in the coloni- 

 zation of rivers. According to A. Derzhavin (1939) these species do not live 

 in the rivers because their plankton larvae are carried away by the current. 

 However, the Caspian Ampharetidae (and the great majority of other members 

 of this family) do not have plankton larvae ; on the other hand the existence 

 of such larvae in the case of Dreissena polymorpha has not prevented the latter 

 from densely populating the whole of the Volga. Colonization by way of 

 passive immigration has been extremely effective for Caspian animals. Cordy- 

 lophora caspia, Victor ella parida, Dreissena polymorpha, Stenogammarus isch- 

 nus and Corophium curvispinum have moved farthest northward, as far as the 

 Baltic Sea. The four forms could easily have been propagated by river-craft. 

 Cordylophora caspia outdistanced the others and at present it is becoming 

 cosmopolitan. It has been found in North and South America, in Australia, 

 New Zealand and China, so far everywhere in large sea ports, where it is 

 brought by ships. However, the last rise in salinity of the Caspian basin 

 after the glacial transgression was not the sole cause of the colonization of 

 the river systems by a number of forms. Such 'waves' of immigration have 

 taken place many times in the history of the south Russian bodies of water. 

 Ya. Birstein and Vinogradov (1934) have noted, in the process of the im- 

 migration of river crayfish, three such ' waves ' even before the isolation of 

 the Caspian Sea from the Black Sea. The fresh-water medusa Craspedacusta 

 is, no doubt, also a very ancient immigrant from some bodies of water, 

 ancestors of the Sarmatian basin (L. A. Zenkevitch, 1940). 



The correlation between the Caspian, Baikal and Okhrida faunas 

 The family ties between the Caspian fauna and those of some very remote 

 bodies of water, in particular those of Lakes Baikal and Okhrida, are evi- 

 dent. The Caspian Porifera Metschnikovia is akin to the Baikal Lubomir. 

 skiidae and the Okhrida Ochridospongia. The gastropod molluscs Micro- 

 melaniinae belong, together with the Baikal Baicaliinae, to one Microme- 

 laniidae family, members of which live elsewhere only in Lake Okhrida. The 

 polychaete genus Manayunkia has some of its forms in Lake Baikal and in 

 the Caspian Sea. Finally a whole number of the Caspian and Baikal sand- 

 hoppers are undoubtedly related ; this was proved not only morphologically 

 but also by the results of the precipitation reaction. In the opinion of A. Mar- 

 tynov (1924) and D. Taliev (1941) the links between the Caspian Sea and Lake 

 Baikal are explained by the migration of some Caspian forms into fresh water 

 in the Tertiary period; they then migrated extensively and reached Lake 

 Baikal, where they have maintained themselves to this day. G. Vereshchagin 

 (1941) thinks 'that the Caspian and Lake Baikal are two centres of the develop- 

 ment of marine fauna which had intruded into inland waters ; moreover the 

 ancestors of these forms, which lived in the pre-Sarmatian Seas on the one 

 hand, and in the east-Asiatic Seas on the other, were not identical, but were 

 similar in different groups in a different way'. Indeed, Vereshchagin thinks 

 that the marine organisms penetrated into the Caspian Sea much later than 

 into Lake Baikal. 



