GENERAL CHARACTERISTICS AND GEOLOGICAL HISTORY 369 



into the Azov-Black Sea basin of the forms of the Caspian fauna living there 

 at present. 



The Azov-Black Sea basin is almost free of the endemic forms of the 

 Caspian fauna (except for Moerisia maeotica (Ostroumovia) among the coe- 

 lenterata, Corophium maeoticum, Hemimysis serrata, Astacus colchicus, Gam- 

 mar us shablensis, Niphargoides intermedins, Stenogammarus compresso-similis 

 among the crustaceans, Percarina among the fishes and Clupenella abrau and 

 Monodacna colorata and M. pontica among the molluscs) ; this is an indi- 

 cation, contrary to widespread opinion, of a very recent penetration of 

 Caspian fauna into the Sea of Azov followed by its settlement in the Black 

 Sea. In the opinion of these workers, this penetration through the Manych 

 Strait should be related to the post-glacial period. P. Dvoichenko (1925), 

 however, had earlier expressed the same point of view for the whole of the 

 Caspian fauna of the Azov-Black Sea basin (migration during the Novo- 

 Euxine period). 



Mordukhai-Boltovskoy relates this migration to the period of the Khvalynsk 

 transgression. Both authors accept the possibility of the mass extinction of 

 Pontic fauna in the Azov-Black Sea basin during the period of greatly in- 

 creased salinity in the Karangat era. 



Taking issue with the two above-mentioned authorities, A. Derzhavin 

 (1951) has noted that 95 species and 50 genera of Ponto-Caspian autoch- 

 thonous forms live in the lower reaches of rivers and in inlets in the northwest 

 part of the Black Sea (from the Danube to the Dnieper), correspondingly 54 

 species and 32 genera live in the rivers and inlets of the Sea of Azov, and 64 

 species (34 genera) in the northern Caspian river basins. Moreover, a large 

 number of autochthonous relict Pontic forms absent from the Volga are 

 found in the rivers and inlets of the Black and Azov Seas. Derzhavin reckons 

 among such forms five genera and seventeen species of fish, six genera and 

 fourteen species of molluscs, two genera and three species of mysids, one 

 genus and ten species of amphipods and one species of decapods. According 

 to Derzhavin in all 46 species (15 genera) absent from the basin of the river 

 Volga, and 43 species (18 genera) absent from the Sea of of Azov live in the 

 river basins of the northwest part of the Black Sea. Moreover, Derzhavin 

 points out the fact that these forms thrive in fresh water and their coloniza- 

 tion of saline water would inevitably have been difficult. If the colonization 

 of the Caspian fauna had proceeded through the Sea of Azov and in a com- 

 paratively recent period, the picture would have been just the opposite. 



Thus, without denying that an exchange of fauna took place in a recent 

 geological period between the Black and Caspian Seas, Derzhavin consider? 

 that an autochthonous fauna of the Pontic type existed in the Black Sea in 

 the pre-Khvalyn period. V. Pauli (1957) supports Derzhavin's opinion on the 

 basis of his examination of the distribution of the mysids of the Black Sea 

 and the Sea of Azov. Seven species of mysids live in the Black Sea and only 

 five in the Sea of Azov. Yu. Markovsky (1953), who considers the 'Caspian' 

 fauna in the inlets of the northwest part of the Black Sea to be a legacy of the 

 Pontic period, is of the same opinion. The facts quoted by Mordukhai- 

 Boltovskoy himself (1958) to some extent contradict his own opinion on the 



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