View source for Centrohelid

{{Short description|Group of algae}}
{{Automatic taxobox
| name = Centrohelids
| taxon = Centroplasthelida
| authority = Febvre‐Chevalier & Febvre, 1984<ref name="Adl 2019"/>
| image = Raphidiophrys contractilis.jpg
| image_caption = ''[[Raphidiophrys contractilis]]''
| subdivision_ranks = Orders
| subdivision_ref = <ref name="Adl 2019"/><ref name="Yogsothothidae"/>
| subdivision =
*[[Pterocystida]]
**[[Raphidista]]
**[[Pterista]]
*[[Panacanthocystida]]
**[[Chthonida]]
**[[Acanthocystida]]
----
{{small|'''Incertae sedis'''}}
*[[Spiculophryidae]]
*''[[Parasphaerastrum]]''
*''[[Heteroraphidiophrys]]''
| synonyms =
* Centroplastiales
* Centrohelina <small>Hartmann 1913</small>
* Centroheliozoa <small>Cushman & Jarvis 1929 sensu Durrschmidt & Patterson 1987</small>
* Centrohelida <small>[[Alfred Kühn|Kühn]] 1926</small><ref>Kühn, A. (1926). ''Morphologie der Tiere in Bildern''. Heft 2: Protozoen. Teil 2. Rhizopoden. Gebrüder Borntraeger: Berlin.</ref>
* Centrohelea {{au|Kuhn 1926 stat. n. Cavalier-Smith 1993}}
}}

The '''centrohelids''' or '''centroheliozoa''' are a large group of [[heliozoa]]n [[protist]]s.<ref name="pmid15148395">{{cite journal |author=Nikolaev SI |title=The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=101 |issue=21 |pages=8066–8071 |date=May 2004 |pmid=15148395 |pmc=419558 |doi=10.1073/pnas.0308602101 |author2=Berney C |author3=Fahrni JF |display-authors=3 |last4=Bolivar |first4=I |last5=Polet |first5=S |last6=Mylnikov |first6=AP |last7=Aleshin |first7=VV |last8=Petrov |first8=NB |last9=Pawlowski |first9=J|doi-access=free }}</ref>  They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth.{{clarify|date=May 2024}}

==Characteristics==
Individuals are unicellular and spherical, usually around 30–80 μm in diameter, and covered with long radial axopods, narrow cellular projections that capture food and allow mobile forms to move about.

A few genera have no cell covering, but most have a gelatinous coat holding scales and spines, produced in special deposition vesicles.  These may be organic or siliceous and come in various shapes and sizes.  For instance, in ''[[Raphidiophrys]]'' the coat extends along the bases of the axopods, covering them with curved spicules that give them a pine-treeish look, and in ''Raphidiocystis'' there are both short cup-shaped spicules and long tubular spicules that are only a little shorter than the axopods.  Some other common genera include ''[[Heterophrys]]'', ''Actinocystis'', and ''[[Oxnerella]]''.

The axopods of centrohelids are supported by [[microtubule]]s in a triangular-hexagonal array, which arise from a tripartite granule called the ''centroplast'' at the center of the cell.  Axopods with a similar array occur in [[gymnosphaerid]]s, which have traditionally been considered centrohelids (though sometimes in a separate order from the others).  This was questioned when it was found they have [[mitochondrion|mitochondria]] with tubular [[crista]]e, as do other heliozoa, while in centrohelids the cristae are flat.  Although this is no longer considered a very reliable character, on balance gymnosphaerids seem to be a separate group.

[[File:2023 Centrohelid.svg|thumb|upright=2|center|{{center|'''Representation of a centrohelid'''}}{{ordered list|[[Pseudopodia#Axopodia|Axopod]]|
[[Microtubule]] bundle|
Kinetocysts, probably help to paralyze prey|
[[Contractile vacuole]], regulates the quantity of water inside a cell|
[[Lipid]] globule|
[[Lysosome]], holds enzymes|
[[Phagosome|Phagocytic vesicle]]|
[[Golgi apparatus]] layer, modifies [[protein]]s and sends them out of the cell|
Exclusion zone|
Centroplast|
Central [[Granule (cell biology)|granule]]|
Scales|
Spicule-forming [[organelle]], spicules are the needle-shaped spines on the surface<ref name=spicule>{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/S1434461015001224|title=There and Back Again: Parallel Evolution of Cell Coverings in Centrohelid Heliozoans
|first=Vasily V.|last=Zlatogursky|access-date=2024-11-02|journal=Protist|volume=167|issue=1|date=February 2016|pages=51-66}}</ref>|
[[Silicon dioxide|Silica]] deposition [[Vesicle (biology and chemistry)|vesicle]]|
Digestive vesicle|
[[Nucleolus]]|
[[Cell nucleus|Nucleus]]|
Prekinetocyst|
[[Mitochondria|Mitochondrion]], creates [[Adenosine triphosphate|ATP]] (energy) for the cell (ribbon shaped cristae)|
Prey|
Endoplasm|
[[Ectoplasm (cell biology)|Ectoplasm]]}}]]


== Taxonomy ==
=== History ===
The evolutionary position of the centrohelids is not clear.  Structural comparisons with other groups are difficult, in part because no [[flagellum|flagella]] occur among centrohelids, and genetic studies have been more or less inconclusive.  Cavalier-Smith has suggested they may be related to the [[Rhizaria]],<ref name="pmid12664159">{{cite journal |vauthors=Cavalier-Smith T, Chao EE |title=Molecular phylogeny of centrohelid heliozoa, a novel lineage of bikont eukaryotes that arose by ciliary loss |journal=J. Mol. Evol. |volume=56 |issue=4 |pages=387–396 |date=April 2003 |pmid=12664159 |doi=10.1007/s00239-002-2409-y|bibcode=2003JMolE..56..387C |s2cid=8007933 }}</ref> but for the most part they are left with uncertain relations to other groups. A 2009 paper suggests that they may be related to the [[Cryptomonad|cryptophytes]] and [[haptophyte]]s (see [[Cryptomonads-haptophytes assemblage]]).<ref>{{Cite journal |author=Burki, F |author2=Inagaki, Y |author3=Bråte, J |author4=Archibald, J. |author5=Keeling, P. |author6=Cavalier-Smith, T |author7=Sakaguchi, M |author8=Hashimoto, T |author9=Horak, A |author10=Kumar, S |author11=Klaveness, D |author11-link=Dag Klaveness (limnologist) |author12=Jakobsen, K.S |author13=Pawlowski, J |author14=Shalchian-Tabrizi, K |year=2009 |title=Large-scale phylogenomic analyses reveal that two enigmatic protist lineages, Telonemia and Centroheliozoa, are related to photosynthetic chromalveolates |journal=Genome Biology and Evolution |volume=1 |pages=231–238 |doi=10.1093/gbe/evp022 |pmc=2817417 |pmid=20333193 }}</ref> They are currently classified as [[Hacrobia]], under the [[Plants+HC clade]], although some research studies have found evidence against the monophyly of this group.<ref name=ZhaoBurkBratKeel12>{{Cite journal |last1=Zhao |first1=Sen |last2=Burki |first2=Fabien |last3=Bråte |first3=Jon |last4=Keeling |first4=Patrick J. |last5=Klaveness |first5=Dag |last6=Shalchian-Tabrizi |first6=Kamran |year=2012 |title=Collodictyon—An Ancient Lineage in the Tree of Eukaryotes |journal=Molecular Biology and Evolution |doi=10.1093/molbev/mss001 |pmid=22319147 |pmc=3351787 |volume=29 |issue=6 |pages=1557–68}}</ref>
Centrohelids were previously divided into two orders with contrasting scale morphology and ultrastructure: [[Pterocystida]] and [[Acanthocystida]].<ref name="CavalierSmith">{{cite journal|last=Cavalier-Smith|first=Thomas|author2=Chao, Ema E.|year=2012|title=Oxnerella micra sp. n. (Oxnerellidae fam. n.), a Tiny Naked Centrohelid, and the Diversity and Evolution of Heliozoa|journal=Protist|volume=163|issue=4|pages=574–601|doi=10.1016/j.protis.2011.12.005|pmid=22317961}}<!--|access-date=2013-04-13 --></ref> Posterior molecular studies of 2018 have rearranged the classification of centrohelids into two taxa: Pterocystida and [[Panacanthocystida]], which includes both Acanthocystida and the genus ''[[Yogsothoth (protist)|Yogsothoth]]''.<ref name="Yogsothothidae"/><ref name="Adl 2019" />
=== Classification ===
The modern classification of centrohelids, as of 2019:<ref name="Yogsothothidae"/><ref name="Adl 2019" />
* '''Centroplasthelida''' {{au|Febvre‐Chevalier & Febvre 1984}} [=Centrohelea {{au|Kühn 1926 sensu Cavalier‐Smith in Yabuki et al. 2012}}; Centroheliozoa {{au|Dürrschmidt & Patterson 1987}}]
** [[Pterocystida]] {{au|Cavalier‐Smith and von der Heyden 2007, emend. Shɨshkin and Zlatogursky 2018}}
*** [[Raphidista]] {{au|Shɨshkin & Zlatogursky 2018}}
**** [[Choanocystidae]] <small>Cavalier-Smith & von der Heyden 2007</small>
***** ''[[Choanocystis]]'' <small>Penard 1904 non Cognetti 1918</small>
**** [[Raphidiophryidae]] <small>Mikrjukov 1996 emend. Cavalier-Smith & von der Heyden 2007</small>
***** ''[[Raphidiophrys]]'' <small>Archer 1867</small> [''Raphidiaphrys'' (sic) Greeff 1869]
*** [[Pterista]] {{au|Shɨshkin & Zlatogursky 2018}}
**** [[Oxnerellidae]] <small>Cavalier-Smith & Chao 2012</small>
***** ''[[Oxnerella]]'' <small>Dobell 1917</small>
**** [[Pterocystidae]] <small>Cavalier-Smith & von der Heyden 2007</small>
***** ''[[Chlamydaster]]'' <small>Rainer 1968</small>
***** ''[[Pseudoraphidocystis]]'' <small>Mikrjukov 1997</small> [''Pseudoraphidiocystis'' (sic)]
***** ''[[Pseudoraphidiophrys]]'' <small>Mikrjukov 1997</small>
***** ''[[Pterocystis]]'' <small>Siemensma & Roijackers 1988 non Lohmann 1904</small>
***** ''[[Raineriophrys]]'' <small>Mikrjukov 2001</small> [''Rainierophrys'' (sic); ''[[Raineria]]'' <small>Mikrjukov 1999 non Osswald 1928 non de Notaris 1838</small>; ''[[Echinocystis]]'' <small>Mikrjukov1997 non Haeckel 1896 non Bhatia & Chatterjee 1925 non Torrey & Gray 1840 non Gregory 1897</small>]
**** [[Heterophryidae]] <small>Poche 1913</small>
***** ''[[Heterophrys]]'' <small>Archer 1869</small>
***** ''[[Parasphaerastrum]]'' <small>Mikrjukov 1996</small>
***** ''[[Sphaerastrum]]'' <small>Greeff 1873</small>
** [[Panacanthocystida]] {{au|Shɨshkin & Zlatogursky 2018}}
*** [[Chthonida]] {{au|Shɨshkin & Zlatogursky 2018}}
**** [[Yogsothothina]] {{au|Shɨshkin & Zlatogursky 2018}}
***** [[Yogsothothidae]] {{au|Shɨshkin & Zlatogursky 2018}}
****** ''[[Yogsothoth (protist)|Yogsothoth]]'' {{au|Shɨshkin & Zlatogursky 2018}}
*** [[Acanthocystida]] <small>Cavalier-Smith 2011</small>
**** [[Marophryina]] <small>Cavalier-Smith 2011</small>
***** [[Marophryidae]] <small>Cavalier-Smith & von der Heyden 2007</small>
****** ''[[Marophrys]]'' {{au|Cavalier-Smith & von der Heyden 2007}}
**** [[Chalarothoracina]] <small>Hertwig & Lesser 1874 stat n. Cavalier-Smith 2011</small>
***** [[Raphidocystidae]] {{au|Zlatogursky in Zlatogursky et al., 2018}}
****** ''[[Raphidocystis]]'' <small>Penard 1904</small> [''Raphidiocystis'' (sic) Doflein 1928 ; ''Rhaphidocystis'' (sic)]
***** [[Acanthocystidae]] <small>Claus 1874 emend. Cavalier-Smith & von der Heyden 2007</small>
****** ''[[Acanthocystis]]'' <small>Carter 1863 non Kuehner 1926 non Bather 1889 non Haeckel 1896 nomen nudum</small>
** Incertae sedis Centroplasthelida:
*** ''[[Parasphaerastrum]]'' <small>Mikrjukov 1996</small>
*** ''[[Heteroraphidiophrys]]'' <small>Mikrjukov & Patterson 2000</small>{{efn|''Heteroraphidiophrys'', mentioned by Mikrjukov in 2002, was never formally introduced and needs to be avoided; the organism designated needs to be re‐isolated, carefully studied and provided with formal description.<ref name="Adl 2019" />}}
*** [[Spiculophryidae]] {{au|Shɨshkin & Zlatogursky 2018}}
**** ''[[Spiculophrys]]'' <small>Zlatogursky 2015</small>

==Notes==
{{notelist}}

== References ==
{{Reflist|refs=

<ref name="Adl 2019">{{cite journal|vauthors=Adl SM, Bass D, Lane CE, Lukeš J, Schoch CL, Smirnov A, Agatha S, Berney C, Brown MW, Burki F, Cárdenas P, Čepička I, Chistyakova L, del Campo J, Dunthorn M, Edvardsen B, Eglit Y, Guillou L, Hampl V, Heiss AA, Hoppenrath M, James TY, Karnkowska A, Karpov S, Kim E, Kolisko M, Kudryavtsev A, ((Lahr DJG)), Lara E, Le Gall L, Lynn DH, Mann DG, Massana R, ((Mitchell EAD)), Morrow C, Park JS, Pawlowski JW, Powell MJ, Richter DJ, Rueckert S, Shadwick L, Shimano S, Spiegel FW, Torruella G, Youssef N, Zlatogursky V, Zhang Q|year=2019|title=Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes|journal=Journal of Eukaryotic Microbiology|volume=66|issue=1 |pages=4–119|doi=10.1111/jeu.12691|pmid=30257078 |pmc=6492006 }}</ref>

<ref name="Yogsothothidae">{{cite journal|first1=Yegor|last1=Shɨshkin|first2=Daria|last2=Drachko|first3=Vladimir I.|last3=Klimov|first4=Vasily V.|last4=Zlatogursky |date=November 2018|title=''Yogsothoth knorrus'' gen. n., sp. n. and ''Y. carteri'' sp. n. (Yogsothothidae fam. n., Haptista, Centroplasthelida), with notes on evolution and systematics of centrohelids|journal=Protist|volume=169|issue=5|pages=682–696|doi=10.1016/j.protis.2018.06.003}}</ref>

}}

== Further reading ==
{{refbegin}}
* {{cite journal |author=Patterson DJ |title=The Diversity of Eukaryotes |journal=Am. Nat. |volume=154 |issue=S4 |pages=S96–S124 |date=October 1999 |pmid=10527921 |doi=10.1086/303287 |s2cid=4367158 |url=http://www.journals.uchicago.edu/cgi-bin/resolve?AN991002|url-access=subscription }}
{{refend}}

{{Eukaryota|D.}}
{{Cryptophyta and haptophyta}}
{{Taxonbar|from=Q1185812}}

[[Category:Haptista]]
[[Category:Amoeboids]]