Volvocales
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| Volvocales | ||||||||
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The Volvocales are an order of flagellate or pseudociliate green algae which form planar or spherical colonies. These vary from Gonium (4 to 32 cells) up to Volvox (500 cells or more). Each cell has two flagella, and is similar in appearance to Chlamydomonas, with the flagella throughout the colony moving in coordination.
Both asexual and sexual reproduction occur. In the former, cells divide until they form new colonies, which are then released. In the smaller forms typically all cells are involved, but larger forms have anterior vegetative and posterior reproductive cells. Sexual reproduction varies from isogamy (both genders produce flagellate gametes of equal size) to oogamy (one gender produces a much larger, non-motile gamete).
The classification of the Volvocales varies. Very often they are taken to include the orders Chlamydomonadales and Dunallielales, which contain closely related unicellular flagellates, as suborders.