Micromonas

Micromonas is a genus of green algae in the family Mamiellaceae.

Micromonas is a widespread prasinophyte alga that is very small in size, motile, and phototactic. Before characterization and naming of a second species, Micromonas commoda through genome analysis, Micromonas pusilla was considered to be the only species in the genus. This led to a disproportionate amount of research discussing a single species and the suggestion that it was the dominant photosynthetic picoeukaryote in some marine ecosystems. Unlike many marine algae, this single species was thought to be distributed widely in both warm and cold waters, but genome sequencing confirmed indications from single-gene studies that its global distribution really reflected presence of multiple species occupying different niches in the ocean.

Some studies have divided Micromonas pusilla into 3 to 5 different clades despite their similarity in morphologies and habitats. Varying ratios of clades contribute to the M. pusilla population throughout the marine ecosystem leading to the hypothesis of clades arising based on niche occupation and susceptibility to virus infection. Other studies have established the presence of at least seven phylogenetically distinct species for which global sequence analyses are beginning to delineate clear differences in the ocean regions they inhabit, with only some of the species actually co-occurring in the same environment.