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



sampling in one litre of water with a biomass of about 300 mg/m 3 . Ponto- 

 sphaera is just as abundant in the plankton of other areas of the Black Sea, 

 especially just off-shore. 



This author sees a similarity between the phytoplankton of the Black Sea 

 and that of the North Sea, the Norwegian fjords, and the bays of sub-Arctic 

 and Arctic seas, as well as that of the Caspian and Aral Seas. 



Among the diatoms the following genera are richest in species : Chaeto- 

 ceros, Coscinodiscus, Rhizosolenia and Melosira, and among the Dino- 

 flagellata-Peridinium, Dinophysis, Gonyaulax and Ceratium. 



Of the individual species the most significant among the diatoms are Skele- 

 tonema costatum, Chaetoceros radians, Cerataulina bergonii, Leptocylin- 

 drus danicus, Thalassionema nitzschioides, Rhizosolenia calcar-avis, Rh. 

 fragilissima. Among the Dinoflagellata the most important are Prorocentrum 

 micans, Gonyaulax cordata, the species Glenodinium, Exuviella cordata and 

 some species of Peridinium, Ceratium tripos, C. furca and C. fusus. The pre- 

 sence of a large number of fungi, at various stages of development, through- 

 out the upper (down to 300 m) layer of the Black Sea has been discovered 

 during the study of its phytoplankton by N. Morozova-Wodjanitzkaja (1957). 



Qualitative composition of zooplankton. The zooplankton of the Black Sea 

 is poorer in species and has the composition given in Table 161. 



Table 161 



[ * L. Rossolimo (1922) gives 25 species and varieties of Tintinnoidea for the Black Sea 

 t The data in brackets are the numbers of species in the Mediterranean fauna. 

 % For the open sea and its parts of lower salinity M. Galadzhiev (1948) records 22 



species of Rotifera. 



Apart from the forms mentioned, a large number of eggs and larvae of 

 various pelagic and bottom invertebrates and fish are found among the Black 

 Sea plankton during certain periods of the year. The difference between the 

 Mediterranean plankton and that of the Black Sea lies in the absence of 



