Astrephomene

Astrephomene is a colonial, flagellated green alga, consisting of 16, 32, 64 or 128 cells arranged at the periphery of a gelatinous matrix. Two to seven cells are somatic cells (also termed rudder cells); they are small and oriented such that their flagella form a rudder. Cells are spherical or lenticular (lens-shaped), and each cell contains an eyespot, two flagella, several contractile vacuoles at the anterior end, and a large cup-shaped chloroplast. Each cell is surrounded by a gelatinous sheath and adjacent cells are attached to each other by their sheaths, forming a hollow, ovoid or spheroidal colony.

Astrephomene gubernaculifera can reproduce sexually or asexually. During asexual reproduction, rotation of daughter protoplasts occurs in conjunction with the movement of basal bodies during successive cell divisions, ending with the anterior end of all cells of the daughter colony outside after the first nuclear and cytoplasmic division.{{cite journal|pmid=27829356|pmc=5103382|year=2016|last1=Yamashita|first1=S.|last2=Arakaki|first2=Y.|last3=Kawai-Toyooka|first3=H.|last4=Noga|first4=A.|last5=Hirono|first5=M.|last6=Nozaki|first6=H.|title=Alternative evolution of a spheroidal colony in volvocine algae: Developmental analysis of embryogenesis in Astrephomene (Volvocales, Chlorophyta)|journal=BMC Evolutionary Biology|volume=16|issue=1|page=243|doi=10.1186/s12862-016-0794-x |doi-access=free |bibcode=2016BMCEE..16..243Y }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}} This type of asexual reproduction is unique among the colonial volvocine green algae. By contrast, in Eudorina, protoplast rotation is lacking during successive divisions; a spheroidal colony is formed by means of inversion after successive divisions. In sexual reproduction, Astrephomene has two identical mating types (i.e. is isogamous); these fuse to form zygotes.

File:Doi 10.1186-s12862 2016 794 Fig7 HTML.jpg

Astrephomene gubernaculifera is often found in organically rich temporary pools, often in pasture ponds. It typically persists for 1–3 weeks after ponds are formed in beginning of the wet season.{{cite journal|doi=10.1080/00359195409518981|title=Two multicellular motile green algae, Volvulina Playfair and Astrephomene, a new genus|date= 1954|last1= Pocock|first1= M. A.|journal= Transactions of the Royal Society of South Africa|volume= 34|issue= 1|pages= 103–127|bibcode= 1954TRSSA..34..103P}}

It has been collected from South Africa, Australia, the United States, and Japan.

Astrephomene was formerly placed in the monotypic family Astrephomenaceae. Astrephomenaceae is now considered obsolete, and the genus is now classified within the Goniaceae.{{cite journal|last1=Nozaki|first1=H.|last2=Kuroiwa|first2=T.|date=1992|title=Ultrastructure of the extracellular matrix and taxonomy of Eudorina, Pleodorina and Yamagishiella gen. nov. (Volvocaceae, Chlorophyta)|journal=Phycologia|volume=31|issue=6|pages=529–541|doi=10.2216/i0031-8884-31-6-529.1|bibcode=1992Phyco..31..529N }}

Astrephomene consists of two species, Astrephomene gubernaculifera and Astrephomene perforata. The two species differ in the morphology of the cells, such as the shape of their cellular sheaths and presence of pyrenoids.{{cite journal|doi=10.51033/jjapbot.58_11_7555 |date=1983 |volume=58 |last1=Nozaki |first1=Hisayoshi |title= Morphology and taxonomy of two species of Astrephomene (Chlorophyta, Volvocales) in Japan |journal=Journal of Japanese Botany }}

Colony inversion is believed to have arisen twice in the order Chlamydomonadales. Spheroidal colony formation differs between the two lineages: rotation of daughter protoplasts during successive cell divisions in Astrephomene, and inversion after cell divisions in Eudorina.

File:Doi 10.1186-s12862 2016 794 Fig1 HTML.jpg to Volvox, and the other in the genus Astrephomene. All drawings and photographs represent side views of individuals with anterior ends orienting toward the top of this figure. Note that the phylogeny has been revised in newer studies, placing Tetrabaena as sister to the rest of the group.{{Cite journal |last1=Lindsey |first1=Charles Ross |last2=Knoll |first2=Andrew H. |last3=Herron |first3=Matthew D. |last4=Rosenzweig |first4=Frank |date=2024-04-10 |title=Fossil-calibrated molecular clock data enable reconstruction of steps leading to differentiated multicellularity and anisogamy in the Volvocine algae |journal=BMC Biology |volume=22 |issue=1 |pages=79 |doi=10.1186/s12915-024-01878-1 |issn=1741-7007 |pmid=38600528 |doi-access=free|pmc=11007952 |bibcode=2024BMCB...22...79L }}]]

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• {{ cite journal |vauthors=Nozaki H, Onishi K, Morita E | date = 2002 | title = Differences in pyrenoid morphology are correlated with differences in the rbcL genes of members of the Chloromonas lineage (Volvocales, Chlorophyceae) | journal = J Mol Evol | volume = 55 | pages = 414–430 | pmid = 12355262 | doi = 10.1007/s00239-002-2338-9 | issue = 4| bibcode = 2002JMolE..55..414N | s2cid = 19862929 }}

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Category:Chlamydomonadales genera

Category:Chlamydomonadales

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