{{Short description|Group of protists}} {{Automatic taxobox | name = Gymnosphaerida | display_parents = 2 | taxon = Gymnosphaeridae | authority = (Poche, 1913) | subdivision_ranks = Genera | subdivision = * ''Actinolophus''? * ''Berkeleyaesol''? * ''Wagnerella''? * ''Actinocoryne'' * ''Gymnosphaera'' * ''Hedraiophrys'' | synonyms = * Axoplasthelida <small>Febvre-Chevalier, 1984</small> * Axoplastheliales * Gymnidae * Hedraiophryidae * Wagnerellidae <small>Poche 1913</small> }} The '''gymnosphaerids''' (or '''Gymnosphaerida''')<ref name="pmid15148395">{{cite journal |vauthors=Nikolaev SI, Berney C, Fahrni JF, etal |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=8066–71 |date=May 2004 |pmid=15148395 |pmc=419558 |doi=10.1073/pnas.0308602101 |doi-access=free }}</ref> are a small group of heliozoan protists found in marine environments. They tend to be roughly spherical with radially directed axopods, supported by microtubules in a triangular-hexagonal array arising from an amorphous central granule.
==Genera== There are only three genera, each with a single species: ''Gymnosphaera albida'', ''Hedraiophrys hovassei'', and ''Actinocoryne contractilis''.
*''Gymnosphaera albida'' is free-living, usually benthic in shallow water. The cells are round and naked, around 70-100 μm in diameter, and resemble the unrelated ''Actinosphaerium''. The outer cytoplasm, or ectoplasm, forms a distinct layer containing large vesicles. *''Hedraiophrys hovassei'' is larger and lives attached to algae and other objects. The cells have a conical base, and are covered with long siliceous spicules. The ectoplasm is distinct and frothy, and typically contains bacterial and algal endosymbionts. *''Actinocoryne contractilis'' is benthic. When feeding, it has a multinucleate base and a contractile stalk up to 150 μm in length, supporting a relatively small uninucleate head, where the central granule and axopods are located. In order to move, it collapses the stalk and head into an amoeboid form which is capable of migration.<ref>{{cite journal|title=Preliminary study of the motility processes in the stalked heliozoan ''Actinocoryne contractilis'' |author=Febvre-Chevalier C |journal=Biosystems |volume=14 |issue=3–4 |date=1981 |pages=337–343 |pmid=7337812 |doi=10.1016/0303-2647(81)90040-X}}</ref> Reproduction is either by budding off the head or fragmentation of the headless form, producing small free-living cells similar to ''Gymnosphaera'', which then attach themselves and regrow the stalk and base.
==Classification== Gymnosphaerids were originally considered centrohelids, which also have microtubules in a triangular-hexagonal array, but are set apart from the others by the structure of the central granule and the mitochondria, which have tubular cristae. The two groups have been treated as separate orders (Axoplasthelida and Centroplasthelida) in a common class, but this has lost support. Instead the gymnosphaerids may be allied with the desmothoracids, and on account of this have been placed in the Cercozoa, but this is somewhat tentative.
* Order '''Gymnosphaerida''' <small>Poche 1913 emend. Mikrjukov 2000</small><ref>{{cite web| last1=Zicha | last2=Hrb | last3=Maňas |last4=Novák |title = Systema Naturae 2000 / Classification, Species Gymnophrys cometa | year=1999 | publisher =BioLib | url=https://www.biolib.cz/en/taxon/id497139/ | access-date = 9 November 2016}}</ref> ** Family '''Gymnosphaeridae''' <small>Poche 1913</small> *** Genus ''Actinolophus?'' <small>Schultze 1874</small> **** Species ''Actinolophus pedunculatus'' <small>Schulze 1874</small> *** Genus ''Berkeleyaesol?'' <small>Shishkin, Drachko & Zlatogursky 2021</small> **** Species ''Berkeleyaesol magnus'' <small>(O'Donoghue 1922) Shishkin, Drachko & Zlatogursky 2021</small> *** Genus ''Wagnerella?'' <small>Mereschkowsky 1878</small> **** Species ''Wagnerella borealis'' <small>Mereschkowsky 1878</small> *** Genus ''Gymnosphaera'' <small>Sassaki 1894 non BIume 1828</small> **** Species ''Gymnosphaera albida'' <small>Sassaki 1894</small> *** Genus ''Hedraiophrys'' <small>Febvre-Chevalier & Febvre 2005</small> **** Species ''Hedraiophrys hovassei'' <small>Febvre-Chevalier & Febvre 2005</small> *** Genus ''Actinocoryne'' <small>Febvre-Chevalier 1980</small> **** Species ''Actinocoryne contractilis'' <small>Febvre-Chevalier 1980</small>
==References== {{Wikispecies|Gymnosphaerida}} {{Reflist}}
{{Rhizaria}} {{Taxonbar|from=Q575077}}
Category:Amoebas Category:Filosa
{{Cercozoa-stub}}