Light micrograph of the green algae Coelastrum sp. and Spirogyra sp. Coelastrum (right) forms hollow, spherical or polyhedral colonies with mostly 8 to 32 cells. The colonies are immobile. The cells have a chloroplast and a pyrenoid. Spirogyra (left) forms filamentous colonies and has mural, spiral chloroplasts. Microscopic contrast method : Differential interference contrast. Magnification 700x at a print width of 10 cm.