Table 1. 



21 



Number of species of the Physosomata inhabiting different depths in the Kuril- 

 Kamchatka Trench' (from Vinogradov, 1970) 



Depth, m 





Species 



occurring 







Number of 



Number of 



% of total 



% of number of 





species 



species 



number of 



species found 





encountered 





species 



in given depth 



0-200 



2 



2 



7.7 



100 



200-500 



12 



10 



38.5 



83.5 



500-750 



15 



4 



15.4 



26.5 



750-1,000 



15 















1,000-1,500 



17 



4 



15.4 



23.5 



1,500-2,000 



17 















2,000-2,500 



14 















2,500-3,000 



16 



2 



7.7 



12.5 



3,000-4,000 



14 



4 



15.4 



28.6 



4,000-5,000 



8 















5,000-6,000 



6 















6,000-7,000 



2 















Above 7,000 







— 



— 



— 



'Twenty-six species are considered, for which two or more specimens were found. 



Table 2, Number of species of the Physosomata inhabiting different depths in the Canary 

 Islands region' (from Thurston, 1976b) 



Depth, m 





Species 



occurring 







Number of 



Number of 



% of total 



% of number of 





species 



species 



number of 



species found 





encountered 





species 



in given depth 



0-200 



10 



10 



62.5 



100 



200-500 



13 



4 



25.0 



30.8 



500-750 



11 



2 



12.5 



18.1 



750-1,000 



9 















'Sixteen species are considered, for which two or more specimens were found. 



28 



depths of 2,500-4,000 m abysso-pelagic species appear (nearly 25% of 

 the fauna examined). At these depths lies the lower boundary of the 

 habitat of 12 bathypelagic species (nearly half of the fauna examined). 

 Thus, in terms of changes in the species composition of the Physosomata, 

 three distinct layers are identifiable, which correspond to the mesopelagic 

 (from 200 to 750-1,000 m), bathypelagic (from 1,000 to 2,500-4,000 m), 

 and abyssopelagic (deeper than 2,500-4,000 m). 



In tropical regions of the oceans (Table 2) the role of species inhabit- 

 ing the epipelagic zone increases. Many mesopelagic species rise to even 

 the epipelagic upper 100-200 m layer or even to the surface. However, 



