In
taxonomyAlpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
, the
Volvocales, also known as
Chlamydomonadales, are an
orderIn scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of
flagellateFlagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...
or
pseudociliatePseudociliate is made of two roots,One Greek and one is Latin.Pseudos in Greek means false, cilium in Latin means eyelash....
green algaeThe green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
, specifically of the
ChlorophyceaeThe Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced...
. Volvocales can form planar or spherical colonies. These vary from
GoniumGonium is a genus of colonial algae, a member of the order Volvocales. Typical colonies have 4 to 16 cells, all the same size, arranged in a flat plate, with no anterior-posterior differentiation. In a colony of 16 cells, four are in the center, and the other 12 are on the four sides, three each....
(4 to 32 cells) up to
VolvoxVolvox is a genus of chlorophytes, a type of green algae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox developed its colonial lifestyle .-Description:Volvox is the most developed...
(500 cells or more). Each cell has two flagella, and is similar in appearance to
ChlamydomonasChlamydomonas is a genus of green algae. They are unicellular flagellates. Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics...
, 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
isogamyIsogamy is a form of sexual reproduction that involves gametes of similar morphology , differing only in allele expression in one or more mating-type regions...
(both genders produce flagellate
gameteA gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s of equal size) to
oogamyOogamy is the familiar form of sexual reproduction. It is a form of anisogamy in which the female gamete is significantly larger than the male gamete and is non-motile. The male gametes are typically highly motile spermatozoa competing for the fertilization of the immotile egg.By contrast to...
(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.