Т НЕ WHITE SEA 199 



In its chief habitats N. virens attains 1 m in length. White Sea specimens are 

 20 to 30 cm long. According to fishermen, in spring the heteronereis stages of 

 this polychaete, as big as snakes, sometimes appear in numbers on the sur- 

 face of the water. On the Murman Peninsula individual specimens of N. virens 

 have been found only in its most western part. They have not been caught 

 farther east. It is possible that N. virens in the White Sea is a thermophilic 

 relict ; but it is more probable that it has penetrated here recently in consequence 

 of the general rise in temperature of the Arctic. In late years N. virens has 

 appeared also on the coast of Iceland, and it apparently ought to have been 

 discovered throughout the Murman coast. 



Other forms inhabit the White, Barents and Baltic Seas, but are wholly or 

 partly absent from the coast of Norway and the North Sea. Examples are the 

 Arctic littoral Priapuloidea Halicryptus spinuJosus, the polychaete Rhodine 

 gracilior and others. 



The peculiar distribution of these forms might have been explained even 

 without a direct link between both Seas in the past. When the climate was 

 colder than it is today, many Arctic forms moved far to the south, and may 

 have penetrated into the Baltic Sea through the North Sea. In a later phase, 

 warmer than at present (the Littorina stage), the Arctic forms were shifted 

 far to the north, and more thermophilic forms moved up after them and pene- 

 trated into Cheshskaya Inlet and through the Gorlo into the White Sea. The 

 Baltic Sea, in consequence of the rigorous climatic conditions in its northern 

 and deeper part, preserved Arctic relicts; the White Sea, because of the pecu- 

 liarity of its thermal conditions, preserved both cold-water and warm- water re- 

 licts. But the existence of a direct link between the White and Baltic Seas is not 

 based solely upon zoogeographical data, but also on geological investigations 

 in regions lying between the two Seas. If the direct link has been established 

 then' the merging of the fauna of both may have occurred on a large scale. 

 Thus we find in the White Sea fauna the following elements : 



(7) Forms which also inhabit adjacent parts of the Barents Sea 



(2) Warm-water relicts 



(3) Cold-water relicts 



(4) Forms common to the Baltic Sea 



(5) Forms common to Far Eastern seas 



(6) Endemic forms. 



Thus the White Sea, like the Baltic Sea, and to some extent like the Barents 

 Sea also, is not homogeneous from a zoogeographical point of view. The 

 littoral fauna, as in the Barents Sea, bears a pronounced boreal character, 

 the sublittoral has an Arctic character, and the pseudo-abyssal a pronounced 

 high Arctic aspect. 



History of the fauna. As the result of a detailed analysis of the fauna of the 

 White Sea K. Derjugin (1928) came to the conclusion that ' the whole of it was 

 formed during the period after the last glaciation and the freezing of the 

 White Sea basin in the post-glacial epoch; that is, its age amounts to about 

 13,500 years'. 



