The three species of the genus Ectothiorhodospira have been found to contain the carotenoids of the normal spirilloxanthin series, spirilloxanthin itself being the major component. While the carotenoid composition of E. mobilis and E. shaposhnikovii is not sufficiently different to allow interspecific differentiation, that of E. halophila differs from the two former species by its lack of rhodopin, and its higher amount of spirilloxanthin.