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The Black Sea communicates with the Mediterranean through 

 the Bosphorus and the Sea of Marmara, but the number of species 

 of Crustacea is greatly depleted when compared with the Mediter- 

 ranean. There are, for instance, only four species of barnacles, com- 

 pared with more than 40 in the Mediterranean, and 35 decapods 

 compared with over 200 Mediterranean species. But the Black 

 Sea Crustacea are not to be thought of as merely as a diminished 

 selection of Mediterranean species, even though this is largely true. 

 There is another element in the fauna, known as the Sarmatian 

 relict fauna, which dates from the time when a great inland sea 

 extended from the Caspian to the Black Sea and even into Greece 

 and Jugoslavia. This relict fauna is sometimes called the Caspian 

 element of the Black Sea Fauna. Comparison of the Crustacea from 

 these two seas, together with the Sea of Azov, shows that they have 

 about thirty species in common, which are not found elsewhere. 

 An interesting feature is that most of these species inhabit estuaries 

 in the Black Sea, but live in the open waters of the Caspian. This 

 may be explained by the fact that the average salinity of the 

 Caspian is only two-thirds of that of the Black Sea. Further, the 

 salinity of the Black Sea is only one-half of that of the Mediter- 

 ranean. This provides an explanation of the impoverishment of the 

 Black Sea fauna when compared with the Mediterranean; the 

 reduced salinity acts as a barrier to the immigration of the more 

 strictly marine Crustacea. 



The Caspian is even more isolated than the Black Sea, and has a 

 higher proportion of endemic species. The most striking example 

 of endemism is found among the Cumacea; the family Pseudo- 

 cumatidae has radiated into nineteen distinct Caspian species. Apart 

 from ancient endemic groups there are also a few Crustacea which 

 appear to have come from the Arctic Sea. Mesidotea entomon is 

 a large isopod otherwise found in the Arctic and Baltic Seas, while 

 the amphipod genus Psendalibrotus, with two species in the 

 Caspian, is found in the Arctic Sea, but not in the Baltic. It is 

 thought that at one time a great ice-lake connected the Baltic and 

 the Caspian, and possibly another such lake connected the Caspian 

 with the Arctic in the region of the Kara Sea. These lakes 

 would provide the Arctic fauna with a means of access to the 

 Caspian. 



Recently there have been additions to the Caspian Crustacea 

 which are due to man's activities. Two species of the prawn Leander 

 were deliberately introduced in the early 1930's, and the barnacle 



