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



groupings of the upper horizon of the sublittoral of the Far Eastern Seas. 

 The most characteristic among its accompanying species is Ampelisca macro- 

 cephala, with a population density of some thousands of specimens per m 2 . 



Echinodermata form a continuous cover at the bottom, at times even with 

 two layers. They feed on vegetable detritus which is easily carried over the 

 compact sand and the aboral sides of the bodies of the Echinodermata. 

 Detritus rolls over the ambulacral grooves to the oral side, and is transported 

 into the mouth-opening. 



On the soft soils of the lower horizons of the sublittoral large patches are 

 inhabited by the biocoenosis Ophiura sarsi. 



A. Savilov has worked out a very interesting picture of the ecological dis- 

 tribution of the bottom fauna on the example of the Sea of Okhotsk (1961). 

 His work is based on the relationship between the character of feeding, the 

 nature of the sea-bed and the speed of the current, and comparing these 

 factors with the structure of the body, the organs of digestion and those used 

 for seizing food. 



In his classification of animals according to their manner of feeding Savilov 

 (1961) follows S. Yong (1928), S. Zernov (1949), E. Turpaeva (1948, 1952), 

 J. Allen (1953) and others, distinguishing mobile and sessile sestonophages 

 (on hard and soft beds), mobile and sessile detritus-feeders, which swallow the 

 soil, carnivores and carrion-eaters. Savilov provides a distribution in space, 

 and a quantitative distribution for every ecological group, characterizing in 

 this manner the ecological structure of the bottom-living fauna throughout 

 the Sea of Okhotsk and its separate regions {Tables 318, 319 and 320 and Fig. 

 398). 



Savilov has distinguished the following ecological zones of the benthic 

 fauna in the Sea of Okhotsk (Fig. 398) : 



(1) Zone of predominance of the immobile sestonophages of the hard sub- 

 stratum (Porifera, Hydroidea, Alcionaria, Bryozoa, Cirripedia, Brachio- 

 poda, Ascidia). 



(2) Zone of predominance of the mobile sestonophages of the soft sub- 

 stratum (Cardiidae, Astartidae, Mactridae, Veneridae, Ampeliscidae, Echina- 

 rachnius parmd). 



(2a) Subzone of predominance of the uatsea-\irchm(Ecliinarachnius parma). 



(3) Zone of predominance of the detritus-collecting forms (Tellinidae, 

 Nuculidae, Ledidae, Terebellidae, Ampharetidae, Ophiura spp.). 



(Зв) Subzone of predominance of the detritus-collecting bivalves (Macoma 

 calcarea, Yoldia thraciaeformis, Y. limatula, Leda spp., Nucula spp.). 



(4) Zone of predominance of the bottom feeders (Maldanidae, Capitellidae, 

 Brisaster, Ctenodiscus, Molpadiidae). 



(5) Zone of predominance of the immobile sestonophages of the soft sub- 

 stratum (Pavonaria, Umbellula, Radiceps, Crinoidea, Potamilla symbiotica, 

 Sabellidae, Culeolus, Lamellisabella zachsi). 



The quantitative distribution of the benthos in the Sea of Okhotsk is very 

 irregular (Fig. 399). The densest benthos colonies, with a predominance of 

 fouling fauna, are found off the northern and eastern shores of the Sea, where 



