Class: Bacillariophyceae Pennate diatoms are found in a diverse array of marine environments including pelagic and benthic habitats. As the first pennate diatom to have its genome sequenced1, P. tricornutum has become a model organism for diatom physiology and been used in numerous studies due to its amenability to laboratory cultivation. The genome suggests there may be significant metabolic variation between P. tricornutum and Thalassiosira pseudonana, the only other diatom with a sequenced genome. P. tricornutum is known to tolerate a wide range of salinities and one of the few known diatom species capable of living without forming a silica shell. Cells are ca. 18-26 um in length and 2-3 um wide. 1)Bowler, C., A.E. Allen, J. Badger, J. Grimwood, K. Jabbari, A. Kuo, U. Maheswari, C. Martens, F. Maumus, R.P. Otillar, E. Rayko, A. Salamov, K. Vandepoele, B. Beszteri, A. Gruber, M. Heijde, M. Katinka, T. Mock, et al. (2008). The Phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature 456: 239-244.