Bacillariophyceae is a class of algae which are commonly known as diatoms. These are single celled organisms, whose lengths are measured in microns, that mostly live in open water as part of what is known as the plankton community, but can also form a coating on aquatic bottom structures or a film on the water surface when coming together as a colony. They are good indicators of water quality.

One of the most interesting facts about diatoms is that their outer cell wall is made of silica (hydrated silicon dioxide).