THE BALTIC SEA 



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of bivalves found in the Kattegat exist in the central part of the Baltic Sea, and 

 each of these forms a dense population in separate areas of the Sea. These 

 forms are, in order of decreasing importance : Macoma baltica, My a arenaria, 



Fig. 146. Penetration of some marine and brackish-water animals far into the Baltic 



Sea (Sagerstrale, 1957). 



Cardium edule, Mytilus edulus and Macoma calcarea. Macoma baltica, far 

 and away the most dominant form not only among the molluscs but among 

 the whole fauna, has found in the Baltic Sea exceptionally favourable condi- 

 tions for existence. In the Bornholm area two more bivalves — Astarte ellip- 

 tica (synonym: A. compressa) and A. borealis (a cold-water relict) — should 

 be added to the five given above. Farther to the west, within the transitional 



