Chlorarachniophyte

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Chlorarachniophytes
Chlorarachnion reptans
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Phylum: Cercozoa
Subphylum: Reticulofilosa
Class: Chlorarachniophyceae
Hibberd & Norris, 1984
Orders & Families
Synonyms
  • Chlorarachnea Cavalier-Smith, 1993, orth. zool.
  • Chlorarachniophyta Hibberd & Norris, 1984[1]
A cultured chlorarachniophyte, Lotharella globosa LEX01 strain [2]

The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters.[3] They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally they have the form of small amoebae, with branching cytoplasmic extensions that capture prey and connect the cells together, forming a net. These extensions are dependent on the presence of light and polymerization of the actin cytoskeleton.[4] They may also form flagellate zoospores, which characteristically have a single subapical flagellum that spirals backwards around the cell body, and walled coccoid cells.

The chloroplasts were presumably acquired by ingesting some green alga.[5] They are surrounded by four membranes, the outermost of which is continuous with the endoplasmic reticulum, and contain a small nucleomorph between the middle two, which is a remnant of the alga's nucleus. This contains a small amount of DNA and divides without forming a mitotic spindle. The origin of the chloroplasts from green algae is supported by their pigmentation, which includes chlorophylls a and b, and by genetic similarities. The only other groups of algae that contain nucleomorphs are a few species of dinoflagellates, which also have plastids originating from green algae,[6] and the cryptomonads, which acquired their chloroplasts from a red alga.

The chlorarachniophytes only include five genera, which show some variation in their life-cycles and may lack one or two of the stages described above. Genetic studies place them among the Cercozoa, a diverse group of amoeboid and amoeboid-like[clarification needed] protozoa.

The chlorarachniophytes were placed before in the order Rhizochloridales, class Xanthophyceae (e.g., Smith, 1938), as algae, or in order Rhizochloridea, class Xanthomonadina (e.g., Deflandre, 1956), as protozoa.

So far sexual reproduction has only been reported in two species; Chlorarachnion reptans and Cryptochlora perforans.[3]

Morphology

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Representation of a Chlorarachniophyte
  1. Filopodium
  2. Extrusomes
  3. Mitochondrion, creates ATP (energy) for the cell (flat cristae)
  4. Capping vesicle
  5. Golgi apparatus, modifies proteins and sends them out of the cell
  6. Nucleomorph
  7. Plastid membranes (4, secondary green)
  8. Stacked thylakoid, site of the light-dependent reactions of photosynthesis
  9. Pyrenoid, center of carbon fixation
  10. Globules
  11. Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell
  12. Nucleolus
  13. Nucleus
  14. Prey in phagosome
  15. Digestive vacuole

Phylogeny

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Based on Shiratori et al. 2024.[7]

Chlorarachniophyceae
Chlorarachnea

Taxonomy

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  • Lotharella globosa extending a filopodium (Fp) through a pore of the cell wall (CW) from a walled amoeboid cell. Py: pyrenoid. Scale bar = 10 μm
    Lotharella globosa extending a filopodium (Fp) through a pore of the cell wall (CW) from a walled amoeboid cell. Py: pyrenoid.
    Scale bar = 10 μm
  • Binary and quaternary cell divisions of Lotharella globosa. Arrowheads indicate the parental cell wall. Scale bar = 10 μm
    Binary and quaternary cell divisions of Lotharella globosa. Arrowheads indicate the parental cell wall.
    Scale bar = 10 μm
  • Flagellate cell of Lotharella globosa with a single flagellum (Fl) and plastid (P) Scale bar = 10 μm
    Flagellate cell of Lotharella globosa with a single flagellum (Fl) and plastid (P)
    Scale bar = 10 μm

References

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  1. ^ Hibberd, David J.; Norris, Richard E. (1984). "Cytology and ultrastructure of Chlorarachnion reptans (Chlorarchniophyta Divisio nova, Chlorachniophyceae Classis nova)". Journal of Phycology. 20 (2): 310–330. doi:10.1111/j.0022-3646.1984.00310.x. S2CID 86059445.
  2. ^ Hirakawa; et al. (2011), "Morphological Diversity between Culture Strains of a Chlorarachniophyte, Lotharella globosa", PLOS ONE, 6 (8): e23193, Bibcode:2011PLoSO...623193H, doi:10.1371/journal.pone.0023193, PMC 3156133, PMID 21858028
  3. ^ a b Brodie, Juliet; Lewis, Jane (26 November 2007). Unravelling the algae: the past, present, and future of algal systematics. CRC Press. ISBN 9780849379901.
  4. ^ Avasthi, Prachee; MacQuarrie, Cameron Dale (2022-12-04). "Chlorarachniophytes form light- and Arp2/3 complex-dependent extensions that are involved in motility and predation". Arcadia Science. doi:10.57844/arcadia-eqg7-kf54. ISSN 2998-4084.
  5. ^ Keeling PJ (2009). "Chromalveolates and the evolution of plastids by secondary endosymbiosis". J. Eukaryot. Microbiol. 56 (1): 1–8. doi:10.1111/j.1550-7408.2008.00371.x. PMID 19335769. S2CID 34259721.
  6. ^ Nakayama, Takuro; Takahashi, Kazuya; Kamikawa, Ryoma; Iwataki, Mitsunori; Inagaki, Yuji; Tanifuji, Goro (2020). "Putative genome features of relic green alga-derived nuclei in dinoflagellates and future perspectives as model organisms". Communicative and Integrative Biology. 13 (1): 84–88. doi:10.1080/19420889.2020.1776568. PMC 7518460. PMID 33014260.
  7. ^ a b Shiratori, Takashi; Ishida, Ken-ichiro (March 2024). "Rhabdamoeba marina is a heterotrophic relative of chlorarachnid algae". Journal of Eukaryotic Microbiology. 71 (2): e13010. doi:10.1111/jeu.13010. PMID 37941507.
  8. ^ M.D. Guiry (2016), "Chlorarachniophyceae [Chlorarachnea]", AlgaeBase, World-wide electronic publication, National University of Ireland, Galway, retrieved 25 October 2016
  9. ^ Rogerson, Andrew; Hannah, Fiona J.; Anderson, O. Roger (1998). "A Redescription of Rhabdamoeba marina, an Inconspicuous Marine Amoeba from Benthic Sediments". Invertebrate Biology. 117 (4): 261. doi:10.2307/3227028. JSTOR 3227028. Retrieved 24 April 2024.
  10. ^ Cavalier-Smith (2017), "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences", Protoplasma, 255 (1): 297–357, doi:10.1007/s00709-017-1147-3, PMC 5756292, PMID 28875267
  11. ^ Guiry, M.D.; Guiry, G.M. "Viridiuvalis". AlgaeBase. Retrieved 24 April 2024.
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