Volvox is a chlorophyte green algae found in ponds and ditches, even in shallow puddles. It forms spherical colonies of up to 50,000 cells consisting of two cell types, numerous flagellate somatic cells and a smaller number of germ cells. Somatic cells comprise a single layer with the flagella facing outward and have eyespots that enable the colony to swim towards light for photosynthesis (phototaxis). The colonies are usually organised so that cells with larger eyespots are grouped at one side, and the reproductive cells are grouped at the opposite side.
Volvox diverged from unicellular ancestors approximately 200 million years ago during the Triassic period.
Volvox live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. One of the most-common species, Volvox aureus, can form harmful algal blooms in warm waters with a high nitrogen content.
