Polarised light micrograph of a Fragilaria sp. diatom (rectangle-shaped) and Draparnaldia sp. green algae. Diatoms are a type of single-celled photosynthetic algae that form a significant portion of the Earths biomass. There generate about 20 to 50 per cent of the oxygen produced on the planet each year. Draparnaldia is a genus of filamentous green algae is commonly found in freshwater habitats attached to sand, sticks or rocky substrates. Each filament of Draparnaldia is composed of a chain of cells arranged in one row. Magnification: 186x when printed 10 centimetres wide.