Low temperature scanning electron microscopic photograph of a
sediment surface. The diatoms are packed densely
in several layers. They can reach up to a million cells
per square centimeter
Diatoms are unicellular algae. They are also called "Bacillariophyceae". Most of them have a size of <50 µm, a few reach up to 500 µm and are visible to the naked eye. Diatoms are cosmopolitans. They are found in the sea, in running and stagnant freshwater, in soils and even in the air.