Light micrograph of the filamentous blue-green algae Oscillatoria sp. A small ciliate protozoan is also visible as the small oval body towards lower left. Blue-green algae are considered to be among 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. When surrounded by a gelatinous sheath it is called a filament. Oscillatoria lacks a slimy sheath. The strands of Oscillatoria exhibit a swaying motion & can also move backward & forward. The mechanism for this movement is not yet understood. Magnification: x40 at 35mm, x80 at 5x7cm size.