{{Short description|Group of eukaryotic microorganisms}} {{Automatic taxobox | display_parents = 2 | parent_authority = Cavalier-Smith 2018 | taxon = Helkesida | authority = Cavalier-Smith 2018 | subdivision_ranks = Families | subdivision = *'''[[Sainouroidea]]''' **[[Sainouridae]] *'''[[Helkesimastigoidea]]''' **[[Helkesimastigidae]] **[[Guttulinopsidae]] | diversity = [[#Classification|24 species]] }}
'''Helkesida''' (formerly known as [[Sainouroidea]])<ref name="Cavalier-Smith 2018">{{cite Q|Q53073157}}</ref> is a group of [[microorganism|microscopic]] [[protists]] belonging to the [[supergroup (biology)|supergroup]] [[Rhizaria]], both discovered through [[phylogeny|molecular phylogenetic analyses]]. It contains [[amoeboid]] [[flagellates]] with two [[flagella]]. They are either free-living, mostly on [[feces|fecal matter]], or live inside the [[gastrointestinal tract|gut]] of animals. Among these amoebae, one lineage has independently evolved aggregative [[multicellularity]] similarly to [[slime moulds]].<ref name="Novel diversity in Sainouroidea"/>
==Biology==
The organisms classified as Helkesida commonly have a [[gliding motility]] in which the [[cell (biology)|cell]]s glide on their posterior [[flagellum]]. They are ancestrally [[amoeboid]] bi-[[flagellates]] without scales or [[theca]].<ref name="Adl 2019"/> Unlike most [[Cercozoa]] which have tubular [[crista|mitochondrial cristae]], they can also present flat cristae or discoid cristae. They are the only group within [[Rhizaria]] that present discoid mitochondrial cristae.<ref name="Aggregative multicellularity"/>
These organisms have an amorphous apical [[centrosome]] attached to the nucleus by a [[rhizoplast]]. The [[wikt:kinetid|kinetid]] arises from 2–4 very short [[centriole]]s with dense fibrous roots that attach them to each other and to the nucleus. Their anterior flagellum is reduced to a stub without its 9+2 [[axoneme]]. The centrosome also generates numerous [[microtubule]]s in larger cells. The [[dictyosome|Golgi apparatus]] is seen attached to the [[nuclear membrane|nuclear envelope]] and the anterior rhizoplast. They have a microbody attached to the posterior end of the [[nucleus (cell)|nucleus]].<ref name="Helkesimastix marina"/>
One helkesid genus, ''[[Guttulinopsis]]'', represents an independent lineage in which aggregative [[multicellularity]] has [[evolution|evolved]] to generate "fungi-like" fruiting bodies called [[sorocarp]]s, similarly to [[slime moulds]] such as ''[[Dictyostelium]]''.<ref name="Aggregative multicellularity"/>
==Ecology==
The helkesid [[amoebae]] are [[bacterivore]]s that can be free-living, mostly associated to [[feces|fecal environments]], or [[wikt:endozoic|endozoic]], associated to [[animal]]s.<ref name="Coprophilic amoeboflagellates"/> They thrive in [[Aerobic organism|aerobic conditions]] and the [[microaerophile|microaerophilic]] [[gastrointestinal tract|gut environment]] of animals. ''[[Rosculus]]'' can thrive in [[Anaerobic organism|anaerobic]] culture. It is unknown if their preferred habitat is free-living or endozoic.<ref name="Novel diversity in Sainouroidea"/>
Some host species can harbor different helkesid genera and species. One animal can be infected by multiple species simultaneously, and one species can also infect different animal hosts. More sampling of hosts, amoebae and molecular data is needed to better understand the life history and ecology of these protists.<ref name="Novel diversity in Sainouroidea"/>
==Evolution and systematics==
=== History ===
Helkesida is a group initially named Sainouroidea. It was discovered in 2009 as a highly divergent clade within [[Cercozoa]] through [[phylogeny|phylogenetic analyses]] that used the [[DNA sequencing|sequencing]] of [[18S ribosomal RNA]] from ''[[Cholamonas cytrodiopsidis]]'', ''[[Sainouron acronematica]]'' and ''[[Helkesimastix marina]]''. It is a molecularly diverse clade that branches within a group of ancestrally [[amoeboid]] bi-[[flagellates]] that usually lack an outer cell coat, known as [[Monadofilosa]].<ref name="Helkesimastix marina"/> A 2016 study revealed a previously unknown wide diversity of Sainouroidea in fecal environments. Previous [[environmental DNA|environmental samplings]] excluded sequences from Sainouroidea due to their highly divergent 18S rDNA sequences.<ref name="Coprophilic amoeboflagellates"/> A 2018 study described several new genera and species.<ref name="Novel diversity in Sainouroidea"/>
The initial name for this group, Sainouroidea, had the ''-oidea'' suffix for superfamilies, but it was not assigned to any existing classes or orders due to the uncertainty of its phylogenetic position.<ref name="Helkesimastix marina"/> In a 2018 revision, the class '''Helkesea''' and order '''Helkesida''' were created as a substitute for this name. Sainouroidea was then modified to only include one of the three helkesid families, [[Sainouridae]]. A second superfamily, [[Helkesimastigoidea]], was created to host the remaining two families, [[Helkesimastigidae]] and [[Guttulinopsidae]].<ref name="Cavalier-Smith 2018"/>
===Classification===
{{cladogram|title=Phylogeny of Helkesida |{{clade|style=font-size:90%; |1={{clade |1=''[[Cholamonas]]'' |2={{clade |1=''[[Sainouron]]'' |2={{clade |1={{clade |1=''[[Acantholus]]'' |2=''[[Homocognata]]'' }} |2={{clade |1=''[[Helkesimastix]]'' |2={{clade |1=''[[Puppisaman]]'' |2={{clade |2=''[[Rosculus]]'' |1={{clade |1=''[[Olivorum]]'' |2={{clade |label1=multicellularity |1=''[[Guttulinopsis]]'' }} }} }} }} }} }} }} }} }} |caption=Cladogram of Helkesida, based on a [[18S ribosomal RNA|18S rDNA]] phylogenetic analysis within a 2018 study.<ref name="Novel diversity in Sainouroidea"/> The study names this group "Sainouroidea" due to being published prior to the taxonomic change to Helkesida.<ref name="Cavalier-Smith 2018"/> }}
Currently, Helkesida contains 24 [[species]] distributed in 9 [[genus|genera]], 3 [[Family (taxonomy)|families]]<ref name="Adl 2019"/> and 2 [[superfamily (biology)|superfamilies]].<ref name="Cavalier-Smith 2018"/> Additionally, many [[Operational taxonomic unit|OTU]]s found through [[environmental DNA|environmental sequencing]] may represent undescribed clades.<ref name="Aggregative multicellularity"/><ref name="Coprophilic amoeboflagellates"/>
* Superfamily [[Sainouroidea]] {{au|Cavalier-Smith et al. 2009 emend. 2018}} ** Family [[Sainouridae]] {{au|Cavalier-Smith 2008}} ***''[[Acantholus]]'' {{au|Schuler & Brown 2018}}<ref name="Novel diversity in Sainouroidea"/> ****''[[Acantholus ambigus]]'' {{au|Schuler & Brown 2018}} ***''[[Cholamonas]]'' {{au|Flavin, O'Kelly, Nerad & Wilkinson 2000}}<ref name="Cholamonas"/> ****''[[Cholamonas cytrodiopsidis]]'' {{au|}} ***''[[Homocognata]]'' {{au|Schuler, Silberman & Brown 2018}}<ref name="Novel diversity in Sainouroidea"/> ****''[[Homocognata vulgaris]]'' {{au|Schuler, Silberman & Brown 2018}} ***''[[Sainouron]]'' {{au|Sandon 1924}}<ref name="Sainouron"/> ****''[[Sainouron acronematica]]'' {{au|Cavalier-Smith et al. 2008}}<ref name="Sainouron acronematica"/> ****''[[Sainouron mikroteron]]'' {{au|Sandon 1924}} * Superfamily [[Helkesimastigoidea]] {{au|Cavalier-Smith 2018}} **Family [[Helkesimastigidae]] {{au|Cavalier-Smith 2008}} ***''[[Helkesimastix]]'' {{au|Woodcock & Lapage 1915}}<ref name="Helkesimastix faecicola"/> ****''[[Helkesimastix faecicola]]'' {{au|Woodcock & Lapage 1915}} ****''[[Helkesimastix major]]'' {{au|Woodcock 1921}} ****''[[Helkesimastix marina]]'' {{au|Cavalier-Smith 2009}}<ref name="Helkesimastix marina"/> **Family [[Guttulinopsidae]] {{au|Olive 1970}} ***''[[Guttulinopsis]]'' {{au|Olive 1901}}<ref name="Olive 1901"/> ****''[[Guttulinopsis clavata]]'' {{au|Olive 1901}} ****''[[Guttulinopsis erdosi]]'' {{au|Schuler, Silberman & Brown 2018}} ****''[[Guttulinopsis rogosa]]'' {{au|Schuler, Tice, Silberman & Brown 2018}} ****''[[Guttulinopsis stipitata]]'' {{au|Olive 1901}} ****''[[Guttulinopsis vulgaris]]'' {{au|Olive 1901}} ***''[[Olivorum]]'' {{au|Schuler, Tice, Silberman & Brown 2018}}<ref name="Novel diversity in Sainouroidea"/> ****''[[Olivorum cimiterus]]'' {{au|Schuler, Tice, Silberman & Brown 2018}} ***''[[Puppisaman]]'' {{au|Schuler & Brown 2018}}<ref name="Novel diversity in Sainouroidea"/> ****''[[Puppisaman gallanis]]'' {{au|Schuler & Brown 2018}} ***''[[Rosculus]]'' {{au|Hawes 1963}}<ref name="Rosculus ithacus"/> ****''[[Rosculus hawesi]]'' {{au|Schuler, Tice & Brown 2018}} ****''[[Rosculus incognitus]]'' {{au|Schuler & Brown 2018}} ****''[[Rosculus ithacus]]'' {{au|Hawes 1963}} ****''[[Rosculus liberus]]'' {{au|Schuler & Brown 2018}} ****''[[Rosculus macrobrachii]]'' {{au|Aravindan, Kalavati & Sheeja 2002}} ****''[[Rosculus philanguis]]'' {{au|Schuler, Silberman & Brown 2018}} ****''[[Rosculus piscicus]]'' {{au|Schuler, Silberman & Brown 2018}} ****''[[Rosculus terrestris]]'' {{au|Jousset, Bass & Geisen 2016}} ****''[[Rosculus vulgaris]]'' {{au|Schuler, Silberman & Brown 2018}}
==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="Aggregative multicellularity">{{cite journal|vauthors=Brown MW, Kolisko M, Silberman JD, Roger AJ|title=Aggregative Multicellularity Evolved Independently in the Eukaryotic Supergroup Rhizaria|journal=Current Biology|volume=22|issue=12|date=2012|pages=1123–1127|doi=10.1016/j.cub.2012.04.021|pmid=22608512 |s2cid=17510471 |doi-access=free}}</ref>
<ref name="Helkesimastix marina">{{cite journal|vauthors=Cavalier-Smith T, Lewis R, Chao EE, Oates B, Bass D|title=Helkesimastix marina n. sp. (Cercozoa: Sainouroidea superfam. n.) a Gliding Zooflagellate of Novel Ultrastructure and Unusual Ciliary Behaviour|journal=Protist|volume=160|issue=3|date=2009|pages=452–479|doi=10.1016/j.protis.2009.03.003|pmid=19523874 |doi-access=free}}</ref>
<ref name="Novel diversity in Sainouroidea">{{cite journal|vauthors=Schuler GA, Tice AK, Pearce RA, Foreman E, Stone J, Gammill S, Willson JD, Reading C, Silberman JD, Brown MW|title=Phylogeny and Classification of Novel Diversity in Sainouroidea (Cercozoa, Rhizaria) Sheds Light on a Highly Diverse and Divergent Clade|journal=Protist|volume=169|issue=6|date=2018|pages=853–874|doi=10.1016/j.protis.2018.08.002|pmid=30415103 |s2cid=53289638 |url=http://nora.nerc.ac.uk/id/eprint/520809/1/N520809PP.pdf }}</ref>
<ref name="Coprophilic amoeboflagellates">{{cite journal|vauthors=Bass D, Silberman JD, Brown MW, Pearce RA, Tice AK, Jousset A, Geisen S, Hartikainen H|date=2016|title=Coprophilic amoebae and flagellates, including Guttulinopsis, Rosculus and Helkesimastix, characterise a divergent and diverse rhizarian radiation and contribute to a large diversity of faecal-associated protists|journal=Environ Microbiol|volume=18|issue=5 |pages=1604–1619|doi=10.1111/1462-2920.13235|pmid=26914587 }}</ref>
<ref name="Olive 1901">{{cite journal|vauthors=Olive EW|date=1901|title=A Preliminary Enumeration of the Sorophoreæ|journal=Proceedings of the American Academy of Arts and Sciences|volume=37|issue=12|pages=333–344|doi=10.2307/20021671|jstor=20021671 |url=https://www.biodiversitylibrary.org/part/246323 }}</ref>
<ref name="Helkesimastix faecicola">{{cite journal|vauthors=Woodcock HM, Lapage G|date=1915|title=Observations on the life-cycle of a new flagellate, Helkesimastix fæcicola, n. g., n. sp.: Together remarks on the question of syngamy in the trypanosomes|journal=Proc. R. Soc. Lond. B|volume=88|pages=353–370|issue=604|doi=10.1098/rspb.1915.0001}}</ref>
<ref name="Cholamonas">{{cite journal|vauthors=Flavin M, O'Kelly CJ, Nerad TA, Wilkinson G|title=Cholamonas cyrtodiopsidis gen. n., sp. n.(Cercomonadida), an endocommensal, mycophagous heterotrophic flagellate with doubled kinetid|journal=Acta Protozoologica|date=2000|volume=39|issue=1|pages=51–60}}</ref>
<ref name="Rosculus ithacus">{{cite journal|vauthors=Hawes RS|title=On Rosculus ithacus gen. n., sp. n. (Protozoa, Amoebina), with special reference to its mitosis and phylogenetic relations|journal=Journal of Morphology|date=1963|volume=113|issue=2 |pages=139–149|doi=10.1002/jmor.1051130202|pmid=14061990|s2cid=40212732 }}</ref>
<ref name="Sainouron acronematica">{{cite journal|vauthors=Cavalier-Smith T, Lewis R, Chao EE, Oates B, Bass D|title=Morphology and Phylogeny of Sainouron acronematica sp. n. and the Ultrastructural Unity of Cercozoa|journal=Protist|volume=159|issue=4|date=2008|pages=591–620|doi=10.1016/j.protis.2008.04.002|pmid=18583188 }}</ref>
<ref name="Sainouron">{{cite journal|vauthors=Sandon H|title=Some Protozoa from the Soils and Mosses of Spitsbergen. Results of the Oxford University Expedition to Spitsbergen, No. 27|journal=Zoological Journal of the Linnean Society|volume=35|issue=237|date=1924|pages=449–475|doi=10.1111/j.1096-3642.1924.tb00051.x}}</ref> }} {{Rhizaria}} {{Taxonbar|from=Q110225224}}
[[Category:Cercozoa]] [[Category:Taxa described in 2009]]