Polarised light micrograph of Melosira sp. diatoms (orange-green blocks) and filamentous algae (green threads). Filamentous algae are single algae cells that form long visible chains, threads, or filaments. Melosira diatoms are found in freshwater and have uniformly structured valve walls. Diatoms are a type of algae that form a significant portion of the Earths biomass. They generating about 20 to 50 percent of the oxygen produced on the planet each year. Magnification: 186x when printed 10 centimetres wide.