{{Short description|Genus of algae}} {{Automatic taxobox | image = Polytomella agilis.jpg | image_caption = ''Polytomella agilis'' | taxon = Polytomella | authority = Aragão | subdivision_ranks = Species | subdivision = * ''Polytomella agilis'' * ''Polytomella caeca'' * ''Polytomella capuana'' * ''Polytomella magna'' * ''Polytomella papillata'' * ''Polytomella parva'' }}
'''''Polytomella''''' is a genus of green algae in the family Dunaliellaceae. It is widespread in freshwater habitats worldwide.<ref name=AlgaeBase>{{AlgaeBase genus|name=Polytomella|id=44237}}</ref> The algae is actually colourless. It has discarded the ability of photosynthesis, and lives by consuming compounds like acetate, butyrate, and alcohols. Thus, it's one of the rare examples of non-photosynthetic algae.
''Polytomella'' consists of single, cells that lack cell walls. Cells are ellipsoid, pyriform, or globose, and slightly metabolic (flexible). Cells have four anterior flagella arising from a central papilla. The posterior of the cell is usually rounded, rarely pointed or with spine-like extensions. Although classified as an alga, chloroplasts and pyrenoids are absent and cells instead have vestigial leucoplasts. The cell accumulates starch in its cytoplasm. A single stigma and two to four apical contractile vacuoles are typically present. The single nucleus is located in the central or anterior half of the cell.<ref name=Nakada2014>{{cite book|editor-first1=John D.|editor-last1=Wehr|editor-first2=Robert G.|editor-last2=Sheath|editor-first3=J. Patrick|editor-last3=Kociolek |date= 2014 |edition=2 |title= Freshwater Algae of North America: Ecology and Classification |last1= Nakada|first1=Takashi| last2=Nozaki |first2=Hisayoshi |chapter= Chapter 6. Flagellate Green Algae |url= |location= |publisher= Elsevier Inc. |pages=265–313|isbn=978-0-12-385876-4 }}</ref><ref name=AlgaeBase/>
Asexual reproduction occurs by longitudinal, binary division; sexual reproduction is isogamous with the zygotes giving rise to four motile cells.<ref name=AlgaeBase/>
''Polytomella'' is somewhat similar to ''Tetrablepharis'', another colorless alga with four flagella, but ''Tetrablepharis'' has cell walls. Species are distinguished based on morphological characters such as the presence or absence of a papilla, shape of the cells, and position of intracellular features like starch granules.<ref name=Ettl1983>{{cite book|last1=Ettl|first1=H.|editor-last1=Ettl|editor-first1=H.|editor-last2=Gerloff|editor-first2=J.|editor-last3=Heynig|editor-first3=H.|editor-last4=Mollenhauer|editor-first4=D.|date=1983|series=Süßwasserflora von Mitteleuropa|title=Chlorophyta. 1. Teil / Part 1: Phytomonadina|volume=9|publisher=VEB Gustav Fischer Verlag|pages=XIV + 808|isbn= 978-3-8274-2659-8}}</ref>
==Evolution== ''Polytomella'' is a free-living, flagellated, nonphotosynthetic green alga with a highly reduced, linear fragmented mitochondrial genome.<ref>{{cite journal|last1 = Smith|first1 = DR|last2 = Lee|first2 = RW|title = Nucleotide diversity of the colorless green alga Polytomella parva (Chlorophyceae, Chlorophyta): high for the mitochondrial telomeres, surprisingly low everywhere else.|journal = The Journal of Eukaryotic Microbiology|date = 2011|volume = 58|issue = 5|pages = 471–3|pmid = 21762422|doi=10.1111/j.1550-7408.2011.00569.x}}</ref><ref name=Ege>{{cite journal|last1=Inwood|first1=W|last2=Yoshihara|first2=C|last3=Zalpuri|first3=R|last4=Kim|first4=KS|last5=Kustu|first5=S|title=The ultrastructure of a Chlamydomonas reinhardtii mutant strain lacking phytoene synthase resembles that of a colorless alga.|journal=Molecular Plant|date=November 2008|volume=1|issue=6|pages=925–37|pmid=19825593|doi=10.1093/mp/ssn046|pmc=2902904}}</ref> Plastids are still present, but the plastid genome and all associated gene expression machinery has been completely lost.<ref>[https://link.springer.com/article/10.1186/s12915-022-01263-w A new lineage of non-photosynthetic green algae with extreme organellar genomes]</ref><ref>[https://pmc.ncbi.nlm.nih.gov/articles/PMC3982744/ A Plastid without a Genome: Evidence from the Nonphotosynthetic Green Algal Genus Polytomella]</ref> Having transitioned completely to heterotrophy, ''Polytomella'' uses organic acids, alcohols and monosaccharides as its carbon source.<ref name="Ege"/><ref>{{cite journal|last1=Links|first1=J.|last2=Verloop|first2=A.|last3=Havinga|first3=E.|title=Some growth experiments withPolytoma uvella on synthetic media|journal=Antonie van Leeuwenhoek|date=December 1961|volume=27|issue=1|pages=76–80|doi=10.1007/BF02538425}}</ref><ref name=Gittleson>{{cite journal|last1=Cruz|first1=Vidal|last2=Gittleson|first2=Stephen|title=The genus ''Polytomella'': A review of classification, morphology, life cycle, metabolism, and motility|journal=Archiv für Protistenkunde|volume=124|issue=1–2|pages=1–28|url=http://www.sciencedirect.com/science/journal/00039365/124/1-2|accessdate=25 September 2015|doi=10.1016/s0003-9365(81)80001-2|year=1981|url-access=subscription}}</ref>
==References==
{{Reflist|1}}
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Category:Chlamydomonadales Category:Chlamydomonadales genera Category:Freshwater algae
{{Chlorophyceae-stub}}