In taxonomy, Micromonas is a genus of green algae, specifically of the Mamiellaceae. The genus contains a single species, Micromonas pusilla, which is the dominant photosynthetic picoeukaryote in some marine ecosystems. Unlike many marine algae, it is distributed widely in both warm and cold waters. It is a good swimmer and swims towards light.
M. pusilla is infected by a reovirus called Micromonas pusilla reovirus (MpRV).