2000 



WOO 6000 



DEPTH, no 



8000 10000 



Fig. 346. Decreases in numbers of species (percentage 

 basis) in certain groups of marine bottom-living inverte- 

 brates with increase of depth (Zenkevitch, Birstein and 

 Belyaev). A Polychaeta; В Pericardia; С Pogonophora; 

 D Asteroidea ; E Holothurioidea. 



NUM8ER OF SPECI6S 

 I000 



3000 



Д000 



I000 



3000 



5000 



I0000- 



BENTHOS 



.* PLANKTON 



Fig. 347. Diagram of change 



in qualitative composition of 



oceanic plankton and benthos 



with depth (Zenkevitch). 



