A MORPHOMETRIC STUDY OF EURYHALINITY IN MARINE POPULATIONS OF THE CILIATE GENUS EUPLOTES

Twenty different clonal strains of marine and brackish Euplotes, repre senting four morphotypes, were tested for hyposalinity tolerance by a method which gradually acclimated the cells to lower salinity medium. The lowest salinities in which the strains could thrive ranged from 60 % of normal seawater to complete freshwater. The morphological effects of culture medium salinity were also examined for two strains of a sm all ''Euplotes charon'' morphotype, as well as for two mating compatib le ''Euplotes vannus'' strains and several of their exconjugates. Ther e were no differences between the euryhaline strains grown in fresh or saltwater, except for a slight increase in overall cell size in one s train when cultured in freshwater medium. E. vannus strains increased in overall cell size with decreased salinity; also, the dorsal surface of the cells can become disorganized when the cells are cultured in 3 0% normal seawater.