570 



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



Dreissensia polymorpha 

 v. marina 



Dreissensia polymorpha 

 v. fluviatilis 



Dreissensia polymorpha 

 Dreissensia andrussovi 



Dreissensia caspia 



Adacna minima in the 

 Caspian Sea 



Adacna minima in the 

 Aral Sea 



Monodacna edentula 

 Didacna trigonoides 

 Didacna barbot-de-marni 

 Mytilaster lineatus 

 Cardium edule 

 Nereis diversicolor 

 Sindesmia ovata 



so 



25 



30 



35 %> 



Fig. 271. Survival of certain species of bivalves and Nereis in the Caspian Sea 



(Zenkevitch, 1959). 



Negative features of the Caspian fauna 



The negative features of the Caspian fauna, as compared to the fauna of the 

 open seas, consist of the complete depletion of such groups as Radiolaria, cal- 

 carean and horny Poriferae, Siphonophora, true medusae, Anthozoa, Cteno- 

 phorae, Polyclada, nemertinians, echiurids, sipunculids, priapulids, brachio- 

 pods, chaetognaths, pantopods, crabs, chitons, scaphopods, cephalopods, 

 echinoderms, Enteropneusta, tunicates, Acrania, skates, sharks and ceta- 

 ceans. Moreover, many typical marine groups are very poorly represented 

 here, such as, for example, Foraminifera, Poriferae, Hydrozoa, Polychaeta, 

 Bryozoa, Decapoda, Gastropoda and most of the order of bivalves. 



There is a marked preponderance of crustaceans and fish in the fauna of 

 the Caspian Sea, while the majority of the marine groups are absent. 



