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Chlamydomonadales

Description of Volvocida

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Solitary or colonial; flagellated; most freshwater, but also inhabit soil, snow and ice; marine genera and species are rare; a few colourless genera; radial or near-radial external symmetry; glycoprotein-type cell wall present or absent; flagella inserted apically, and without a scaly covering; basal bodies carrying microtubular flagellar roots are either directly opposed (12/6 o'clock) or displaced into the 1/7 o'clock direction; two system II fibres connect the basal bodies with the nucleus and terminate at the nuclear envelope (nucleus-basal body connectors); mitosis is closed, interzonal mitotic spindle collapses at telophase and a phycoplast (an assembly of microtubules oriented in the plane of cytokinesis) develops; sexual reproduction nearly always involves the formation of a dormant zygote and zygotic meiosis; chloroplasts/leucoplasts present, with chlorophylls a and b, chloroplast/leucoplast envelope consists of two membranes, starch (a-1,4 glucan) synthesized in the stroma of the chloroplast/leucoplast; flagella with a stellate structure in the flagellar transitional region; flagella 2 or 4 of similar length and behaviour; the cell wall may become impregnated with iron, manganese or calcium salts; plastid single, mostly cup-shaped; a single pyrenoid is often present located mostly in a basal position (several pyrenoids may occur or pyrenoids may be absent); an eyespot occurs in most species and consists of one to several layers of eyespot lipid globules located inside the chloroplast; nutrition phototrophic or chemo-organotrophic; phagotrophy absent, contractile vacuoles (2-several, rarely 1) usually present; asexual reproduction either by longitudinal division or by zoospores formed through successive divisions of the protoplast within the parental cell wall; sexual reproduction common, isogamous, anisogamous (heterogamous) or oogamous; typically flagellate gametes agglutinate with their flagella which triggers a sequence of events resulting in cell wall lysis, mating structure activation, flagellar deagglutination and sexual fusion; zygote a thick-walled resting stage (hypnozygote), zygote germination involves meiosis and formation of flagellate meiospores.
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Chlamydomonadales

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Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae.[1] Chlamydomonadales can form planar or spherical colonies. These vary from Gonium (four 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.[citation needed]

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 flagellated gametes of equal size) to oogamy (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.

References

  1. ^ See the NCBI webpage on Chlamydomonadales. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}

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Chlamydomonadales: Brief Summary

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Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae. Chlamydomonadales can form planar or spherical colonies. These vary from Gonium (four 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.[citation needed]

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 flagellated gametes of equal size) to oogamy (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.

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