Chlamydomonadales, also known asVolvocales, are anorder offlagellated orpseudociliatedgreen algae, specifically of theChlorophyceae.[1] Chlamydomonadales can form planar or spherical colonies. These vary fromGonium (four to 32 cells) up toVolvox (500 cells or more). Each cell has twoflagella, and is similar in appearance toChlamydomonas, with the flagella throughout the colony moving in coordination.[citation needed]
Bothasexual andsexual 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 fromisogamy (both genders produce flagellatedgametes of equal size) tooogamy (one gender produces a much larger, nonmotile gamete).
The classification of the Chlamydomonadales varies. Very often they are taken to include the orders Volvocales and Dunallielales, which contain closely related unicellular flagellates, as suborders. Colony inversion is believed to have arisen twice in this order. Spheroidal colony formation differs between the two lineages: rotation of daughter protoplasts during successive cell divisions inAstrephomene, and inversion after cell divisions in theVolvocaceae.[2]
Schematic representation of the phylogenetic relationships of the volvocine algae and the parallel evolution of the spheroidal colony. Volvocine algae range from the unicellular Chlamydomonas to the multicellular Volvox through various intermediate forms and are used as a model for research into the evolution of multicellularity. The spheroidal colony is thought to have evolved twice independently within this group: once in the Volvocaceae, fromPandorina to Volvox, and the other in the genus Astrephomene. The phylogeny is based on previous reports. All drawings and photographs represent side views of individuals with anterior ends orienting toward the top of this figure.[2]
Traditionally, families and genera within Chlamydomonadales have been classified based on their morphology. However,molecular phylogenetic studies have shown that the evolutionary relationships do not correspond to the traditional taxonomic classifications. Despite this, the families and genera are still in use, because the differences have not been reconciled into a single, useful classification system.[4]
In 2008, Nakadaet al. defined a number of well-supportedclades within Chlamydomonadales usingPhyloCode. Their relationships, as well as a few representative genera and species, are shown below.[4]
^abNakada, Takashi; Misawa, Kazuharu; Nozaki, Hisayoshi (2008). "Molecular systematics of Volvocales (Chlorophyceae, Chlorophyta) based on exhaustive 18S rRNA phylogenetic analyses".Molecular Phylogenetics and Evolution.48 (1):281–291.Bibcode:2008MolPE..48..281N.doi:10.1016/j.ympev.2008.03.016.PMID18430591.
^Watanabe, Shin; Lewis, Louise A. (2017). "Phylogenetic interpretation of light and electron microscopic features of selected members of the phylogroupMoewusinia (Chlorophyceae), with new generic taxonomy".Phycologia.56 (3):329–353.Bibcode:2017Phyco..56..329W.doi:10.2216/16-64.1.
^Demchenko, Eduard; Mikhailyuk, Tatiana; Coleman, Annette W.; Pröschold, Thomas (2012). "Generic and species concepts inMicroglena (Previously theChlamydomonas monadina group) revised using an integrative approach".European Journal of Phycology.47 (3):264–290.Bibcode:2012EJPhy..47..264D.doi:10.1080/09670262.2012.678388.
