A genus of green algae consisting of more than 600 species worldwide, living in marine, freshwater, soil, and even snow environments. They are single celled eukaryotic organisms ranging from 5 to 100 micrometers long which can be roughly spherical, egg shaped, or elliptical. Most species have two flagella (coming out the same side) for swimming. Most of the time they are haploid and reproduce by dividing into two (binary fission); when they are stressed they can form gametes which fuse to form diploid cysts which later divide into four haploid cells. Taxonomically they have been classified under plants, animals, and protists. Several species from this genus are important model organisms for the study of cell biology, molecular biology, genetics, plant physiology, and biotechnology. The species most commonly used in scientific experiments is Chlamydomonas reinhardtii (also known as C. reinhardi or C. reinhardii). For more information, visit The Chlamydomonas Page at the Protist Image Database.