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



(5) Steno- and eury-haline brackish-water forms 



(4) Highly euryhaline organisms, the distribution of which does not depend 

 on water salinity. 



Finally the following classification of brackish water was accepted by the 

 Venetian symposium in 1958 as the most suitable for the Baltic Sea : 



Zone Salinity, % 



Hyperhaline >40 



Euryhaline 40 to 30 



Mixohaline 30 to 0-5 



Mixoeuhaline >30 (less than 



the adjacent 

 euhaline 

 waters) 



(mixo) polyhaline 30 to 18 



(mixo) mesohaline 18 to 5 



(mixo) olyghohaline 5 to 0-5 



Fresh water <0-5 



and further subdivisions for the (mixo) mesohaline and (mixo) oligohaline 

 zones : 



(mixo) mesohaline 



a-meshohaline 18 to 10 



p-mesohaline 10 to 5 



(mixo) oligohaline 

 oc-oligohaline 5 to 3 



(3-oligohaline 3 to 0-5 



However, this scheme is too detailed and therefore difficult to apply in 

 practice. For that reason Remane's classification, given above, is preferable. 



The brackish-water relicts in the Baltic Sea which have retained their 

 Arctic aspect most are : Mesidothea entomon, Limnocalanus grimaldii, Ponto- 

 poreia affinis, Myoxocephalus quadricomis and Phoca hispida. 



However, Mysis mixta, M. relicta, Astarte borealis, Pontoporeia femorata 

 and Halitholus cirratus are very closely akin to them, although in the Arctic 

 regions they do not belong, as the others do, to the preponderant brackish- 

 water forms. The third group — steno- and eury-haline brackish-water 

 animals in the Baltic Sea — comprises a fairly considerable group. 



S. Sagerstrale (1957) includes in the group of true brackish- water organisms 

 of the Baltic Sea (except for the Ice Age relicts and the immigrants from other 

 seas) 1 5 species of plants and 43 species of animals : 



Cyanophyceae Anabaena baltica 



Diatomaceae Thalassiosira baltica, Chaetoceros subtilis, Ch. wighami, 



Synedra tabulata, S. pulchella 

 Rhodophyceae Ceramium tenuicorne 

 Phaeophyceae Ectocarpus confervoides fluviatilis, Portoeirema fluviatile 



