Light microscopy of tiny protozoa feeding around large green Micrasterias algae. Micrasterias is a freshwater desmid alga that appears green as it is filled with chlorophyll, which allows it to obtain food through photosynthesis. It forms the base of the food chain throughout much of the world. Micrasterias displays a bilateral symmetry, with two mirror image semi_cells joined by a narrow isthmus containing the nucleus of the organism. This dual semi_cell structure is unique to the desmid algae. Recorded under Nomarski differential interference contrast illumination.