Filamentous algae (Zygnema sp.) cells with chloroplasts, light micrograph. The Zygnemataceae is a family of filamentous green algae, characterised by unbranched filaments, i.e. formed by a single row of cells (uniseriate structure). Each filament is made up of cells aligned one after the other, separated by a septum (transverse partition). These algae reproduce in a characteristic way by conjugation, a mode of sexual reproduction in which the cellular contents of one filament migrate towards a cell of another filament to form a zygote. One of the distinguishing features of the Zygnemataceae is the varied shape of their chloroplasts, the structures that ensure photosynthesis. For example, the genus Zygnema has star-shaped chloroplasts, Spirogyra has helix-shaped chloroplasts, while in Mougeotia, the chloroplasts look like flattened plates. Magnification: x450 when printed at 10 centimetres wide.