Blue-green algae. Coloured scanning electron micrograph (SEM) of Oscillatoria sp., filamentous blue-green algae. Blue-green algae are considered to be one of the most primitive organisms, dating back to pre-Cambrian times. A single row of cells, such as one of these strands, is called a trichome. The strands of Oscillatoria exhibit a swaying motion and can also move backward and forward. The mechanism for this movement is not yet understood. Magnification: x1175 at 6x7cm size.