Diatoms are single-celled organisms which secrete intricate skeletons. These may be elongate, with a bilateral plane of symmetry, or they may be round and radially symmetrical. Diatoms (class Bacillariophyta) are a type of mainly aquatic, photosynthetic algae. Similar to many other algae, they can live as unicellular organisms, colonial, or filamentous. Unlike most algae, though, they have a solid shells made of silica. Because of such shells, diatoms have major economic importance in industry while also having a major role in biological and chemical processes.