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



(iii) Autochthons of the Arctic region, 28 per cent 



(iv) Species of Pacific Ocean origin, 45 per cent (including circumpolar, 

 amphi-boreal and amphi-arctic). 



Fifty-nine species of echinoderms of the Arctic basin (48 per cent) are not 

 known in the Pacific and have no common roots there. The abyssal fauna of 

 the Polar basin has very little in common with the deep-water fauna of the 

 Pacific ; this is fully explained by the shallowness of the Bering Strait. 



The 34 species of echinoderms (28 per cent) autochthonous for the Arctic 

 basin consist above all of stenobathic-abyssal species (6) and eurybathic- 

 abyssal ones (10). These two groups contain five endemic genera. 



Of the 18 autochthons inhabiting the continental shelf 14 species are limited 

 to the Arctic and 4 are arctic-boreal ones. 



Djakonov distinguishes among the species of Pacific origin (45 per cent) 

 some species (about half) identical with the Pacific ones and other forms 

 which are represented in the Pacific by closely-related species. He divides 

 this group into the : 



Circumpolar, 13 species 



Forms characteristic of the eastern Arctic, 10 species 



Amphi-boreal, 31 species. 



In Djakonov's opinion all these forms came from the Pacific Ocean as 

 early as the post-glacial period and populated the northern shores of North 

 America. 



As an example Djakonov gives the distribution of species of the genus 

 Leptasterias : 



Region No. of Leptasterias species 



Northern part of Pacific 27 



Off the northeastern shores of North America 5 



Off Greenland 2 



Off Scandinavia 3 



Circumpolar 1 



The way described here in which the Arctic was populated by Pacific Ocean 

 forms is considered by several authors as basic. 



IV. TYPOLOGY OF THE BODIES OF WATER OF THE ARCTIC 



BASIN AND THE NORTHERN ATLANTIC 

 A quantitative survey of the marine fauna leads to the problem of the typo- 

 logy of the bodies of water based on biological productivity. 



Beside the fact of it belonging to one or another biogeographical region, 

 characterized by a certain specific population, the most important features 

 which condition the whole type of a body of water and that of the biological 

 productivity developed in it are : 



(7) the nature of the connection between the body of water and the ocean 

 (open bodies of water on the one hand, and closed or semi-closed on 

 the other) 



