class of algae

Diatoms are tiny eukaryotic algae. They are a common type of phytoplankton. Most are single cells, but some form chains or simple colonies.

Diatoms through the microscope.jpg
Marine diatoms
Scientific classification

Diatom cells have a unique cell wall made of silica (SiO2). These walls (called "frustules") take many forms, some quite beautiful and ornate. They usually have two asymmetrical sides with a split between them (hence "diatom").

They are one of two great groups of single-celled organisms in the sea. The other is the coccoliths. Since diatoms are made of silica, and coccoliths are made of calcium carbonate, they do not grow in the same places in the sea. This was first discovered by T.H. Huxley in his voyage on HMS Rattlesnake, 1846–1850. Diatoms are also found in some soils and in some waterways on land.

Living diatoms make about 20 to 50 percent of the oxygen produced on the planet each year.[1][2] They take in over 6.7 billion metric tons of silicon each year from the waters in which they live.[3]

Diatom chloroplasts were probably derived from those of red algae. The fossil record of diatoms starts in strata of the Lower Jurassic, ~185 million years ago. Molecular clock evidence suggests an earlier date for their origin.[4] The entire genomes of two species of diatom have been analysed. The analysis reveals that hundreds of genes in both species came from bacteria.[5]

Diatoms have some practical uses. Diatom communities are a popular tool for monitoring environmental conditions, past and present. They are commonly used in studies of water quality. They are also of interest to nanotechnology.


  1. "The air you're breathing? A diatom made that". Live Science. 11 June 2014. Archived from the original on 30 April 2018. Retrieved 30 April 2018.
  2. "What are diatoms?". Diatoms of North America. Archived from the original on 25 January 2020. Retrieved 28 January 2020.
  3. Treguer, P.; Nelson, D.M.; Van Bennekom, A.J.; Demaster, D.J.; Leynaert, A.; Queguiner, B. (1995). "The silica balance in the world ocean: a reestimate". Science. 268 (5209): 375–9. Bibcode:1995Sci...268..375T. doi:10.1126/science.268.5209.375. PMID 17746543. S2CID 5672525.
  4. Kooistra W.H.C.F. and Medlin L.K. 1996. Evolution of the diatoms (Bacillariophyta): IV. A reconstruction of their age from small subunit rRNA coding regions and the fossil record. Mol. Phylogenet. Evol. 6, 391-407.
  5. Bowler C. et al. 2008. The Phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature 456: 239–244.