Polarised light micrograph of a Batrachospermum sp. algal cell and a Fragilaria sp. diatom. Batrachospermaceae are red algae which live in fresh water. Fragilaria are also a type of algae called diatoms which form filaments of cells. Diatoms form a significant portion of the Earth's biomass, generating about 20 to 50 per cent of the oxygen produced on the planet each year. Magnification: x14 when printed at 10 centimetres wide.