Light micrograph of Zygnema sp. ( Greek zygon, yoke and Greek nema, thread) freshwater filamentous green algae. Zygnema forms unbranched filaments of cylindrical cells with two stellate chloroplasts per cell. Culture material of the Culture Collection of Algae at the University of Cologne. Microscopic contrast method : Differential interference contrast. Magnification 580x when printed at 10 centimetres wide.