Limited Hctcrotrophy of Some Photosynthelie Dinojlagellales 109 



These stock media save time in screening newly-collected 

 organisms. One or more of these media will generally support 

 growth and so serve to establish clonal bacteria-free cultures. 



SALINITY TOLERANCE 



Peridiniiim balticnm and P. chattoni are stenohaline brackish 

 organisms. While motile for a long time at seawater concentra- 

 tion, they divide only in more dilute media. The optimal con- 

 centration is one- third to one-fourth seawater (0.8-1.2% salin- 

 ity), the upper limit being 2.0 per cent (14). F. halficiim was 

 thought to be euryhaline ( 1 ) because it was found in ponds 

 ranging from brackish to seawater. The seeming discrepancy 

 may be explained by our observation that it stays motile at 

 0.05-3.5 per cent salinity. ASPi medium diluted to one-third or 

 other media diluted to 1 per cent salinity are adequate media. 

 ExuviaeUa cassubica, obtained from the same brackish pool, is on 

 the contrary euryhaline; it grows in salinities from 0.08 to 3.5 

 per cent. Growtli is better in media of 1-2 per cent salinity (i.e. 

 half-strength ASP^ or ASPi ) . The other species of dinoflagellates 

 have an optimal salinity between 2.0-2.5 per cent, the limits 

 ranging from 1.5 to 4.0 per cent. 



AUXOTROPHY, PHOTOAUTOTROPHY, AND 

 HETEROTROPHIC ABILITIES 



The aforementioned dinoflagellates, like many other photo- 

 synthetic algae, need one or more vitamins. All need Bn'; 

 Amphidinium carteri and A. rhynchocephalum also require biotin 

 and thiamine. 



Specificity toward various cobalamins differs slightly among 

 the various species. All utilize the dichlorobenzimidazole and 

 benzimidazole analogues, and Factor III (5-hydroxybenzimi- 

 dazole); they do not utilize pseudo Bu and Factor B(Bi2 minus 

 nucleotide). The three Gyrodinium do not utilize Factor A (2- 

 methyladenine ) nor Factor H ( 2-metln Ihypoxanthine ) which are 

 utilized by the two Amphidinium; Factor A is also utilized by P. 

 balticum and E. cassubica. The specificity of G. splendens and 

 P. chattoni was not determined. 



The activity of the utilizable cobalamins measured as final 



