Phototaxis in the Unicellular Red Algae Cyanidioschyzon merolae and Cyanidium caldarium

Phototaxis of 2 cyanidiaceae, Cyanidioschyzon merolae and Cyanidium caldarium, was studied by population experiments. We found that cells of both C. merolae and C. caldarium moved towards light in liquid medium, but that the degree of migration was quite different. When laterally illuminated, most of the C. merolae cells moved towards light at a velocity of 0.27 mm/h. In contrast, only a small proportion of C. caldarium cells showed migration towards light and most of the cells remained dispersed. The exterior cell surface of C. merolae was observed by scanning electron microscopy. It appeared thick and flexible enough to enable crawling movement.