The zygnema is a filamentous algae floating on surface of water. The filament in the zygnema is unbranched and the cells are joined end to end. Each cell are rectangular in shape which has the outer pectic layer and the inner cellulosic layer. The filament is completely covered with mucilage and inner to the cell wall is the cell membrane and the protoplasm. At the center of the protoplast lies the single nucleus with two stellate chloroplast on either side of the nucleus. Each chloroplast contains one pyrenoids.