Volvocophyceae

a class of single-celled or colonial green algae that are mobile in the vegetative state. The cells of Volvocophyceae have mostly cup-shaped chromatophores with a pyrenoid, a nucleus, a red eyelet, pulsating vacuoles, and two (more rarely, four to eight) identical flagella. Some single-celled Volvocophyceae are known to have a palmella-like state (an accumulation of individual cells covered with mucus) and cysts. Colonial Volvocophyceae are globular or lamellar. Asexual propagation in single-celled Volvocophyceae lacking a membrane takes place by longitudinal cell division. In single-celled organisms with a membrane, it is accomplished by zoospores and in colonial organisms by successive cell divisions in the maternal colony. Sexual reproduction takes the form of copulation between the vegetative cells or the gametes (isogamy, heterogamy, oogamy). The development of the zygote after a period of rest includes meiosis. Volvocophyceae live mainly in stagnant bodies of fresh water or in the soil. When they grow in massive numbers, they color the water. The USSR has 52 genera (250 species) of Volvocophyceae.