Chlamydomonas

thumb|Drawings of Chlamydomonas caudata Wille. alt=|thumb|330px|Cross section of a Chlamydomonas reinhardtii cell thumb|Light micrograph of Chlamydomonas with two flagella just visible at bottom left thumb|Chlamydomonas globosa, again with two flagella just visible at bottom left

Chlamydomonas ( ) is a genus of green algae consisting of about 150 species of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as "snow algae". Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics. One of the many striking features of Chlamydomonas is that it contains ion channels (channelrhodopsins) that are directly activated by light. Some regulatory systems of Chlamydomonas are more complex than their homologs in Gymnosperms, with evolutionarily related regulatory proteins being larger and containing additional domains.