318 



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



Syndesmya alba are poorly represented here. Among the worms the following 

 may be noted : Nephthys ciliata, Scoloplos armiger, Nereis diversicolor, Pygos- 

 pio elegans, Terebellides stromi, Harmothoe sarsi, Halicryptus spinulosus; 

 among the crustaceans: Diastylis rathkei, Pontoporeia femorata, Bathyporeia 

 pilosa and, in altogether negligible numbers, Mesidothea entomon. The last 

 named, like Pontoporeia affinis, has its western limit of distribution east of 

 Mecklenburg Bay, becoming a mass form to the east and north. On the other 



Fig. 152. Distribution of Macoma biocoenosis in southern Baltic Sea (Demel and 



others, 1954). 



hand such forms as Mya, Cardium and Mytilus gradually disappear as one 

 moves eastward. 



K. Demel and his collaborators W. Mankowski and Z. Mulicki (1951, 

 1954) as a result of comprehensive investigations over a number of years/were 

 able to draw a very interesting picture of the qualitative and quantitative dis- 

 tribution of the bottom fauna of the southern part of the Baltic Sea (south of 

 56° 45'). Demel reports that the Macoma baltica biocoenosis covers the whole 

 of the shallow zone of the southern part of the Baltic Sea (Fig. 152). In deeper 

 places Macoma baltica gradually disappears and is replaced by the biocoenosis 

 of worms (Scoloplos armiger, Halicryptus spinulosus, Priapulus caudatus) 

 and crustaceans (Pontoporeia femorata and Diastylis rathkei) (Fig. 153). 

 Demel thinks that the propagation of Macoma baltica into the depths is limited 

 by the lack of oxygen. In the greatest depths of the Gotland depression colonies 

 of Scoloplos armiger alone have been discovered. The region inhabited by 



