{{Short description|Class of flagellates}} {{Use dmy dates|date=May 2022}} {{Automatic taxobox | image = Calkinsia aureus (2843250035).jpg | image_caption = ''Calkinsia aurea'' | taxon = Symbiontida | authority = Yubuki ''et al.'', 2009<ref>{{Cite journal |last1=Yubuki |first1=Naoji |last2=Edgcomb |first2=Virginia P. |last3=Bernhard |first3=Joan M. |last4=Leander |first4=Brian S. |date=2009-01-27 |title=Ultrastructure and molecular phylogeny of Calkinsia aureus: cellular identity of a novel clade of deep-sea euglenozoans with epibiotic bacteria |journal=BMC Microbiology |volume=9 |issue=1 |pages=16 |doi=10.1186/1471-2180-9-16 |doi-access=free |pmid=19173734 |issn=1471-2180 |pmc=2656514}}</ref> | subdivision_ranks = Families<ref>{{Cite journal |last=Kolisko |first=Martin |last2=Flegontova |first2=Olga |last3=Karnkowska |first3=Anna |last4=Lax |first4=Gordon |last5=Maritz |first5=Julia M. |last6=Pánek |first6=Tomáš |last7=Táborský |first7=Petr |last8=Carlton |first8=Jane M. |last9=Čepička |first9=Ivan |last10=Horák |first10=Aleš |last11=Lukeš |first11=Julius |last12=Simpson |first12=Alastair G. B. |last13=Tai |first13=Vera |date=2020-11-20 |title=EukRef-excavates: seven curated SSU ribosomal RNA gene databases |url=https://academic.oup.com/database/article/doi/10.1093/database/baaa080/5996027?guestAccessKey= |journal=Database: The Journal of Biological Databases and Curation |language=en |volume=2020 |issue=1 |doi=10.1093/database/baaa080 |issn=1758-0463 |via=Oxford Academic |doi-access=free|pmc=7678783 }}</ref><ref name="Cavalier-Smith2"/> | subdivision = *'''[[Postgaardida]]''' **[[Postgaardi|Postgaardidae]] **[[Calkinsia|Calkinsiidae]] *'''[[Bihospites|Bihospitida]]''' **[[Bihospites|Bihospitidae]] | synonyms = *Postgaardia <small>Cavalier-Smith, 2016</small> *Postgaardea <small>Cavalier-Smith, 1998 s.s.</small> }}
'''Symbiontida''' is a [[Basal (phylogenetics)|basal]] [[Class (biology)|class]] of [[flagellate]] [[Euglenozoa]].<ref name="Cavalier-Smith">{{cite journal |doi=10.1016/j.ejop.2016.09.003| title=Higher classification and phylogeny of Euglenozoa | year=2016 | last1=Cavalier-Smith | first1=Thomas | journal=European Journal of Protistology | volume=56 | pages=250–276 | pmid=27889663 | doi-access=free }}</ref><ref name="Kostygov-2023">{{Cite journal |last1=Kostygov |first1=Alexei Y. |last2=Karnkowska |first2=Anna |last3=Tashyreva |first3=Daria |last4=Maciszewski |first4=Kacper |last5=Lukeš |first5=Julius |date=2021 |title=Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses |journal=Open Biology |volume=11 |issue=3 |doi=10.1098/rsob.200407 |doi-access=free|pmid=33715388 |name-list-style=amp |pmc=8061765 }}</ref> As euglenozoans may be basal [[eukaryote]]s, the Symbiontida may be key to studying the evolution of [[Eukaryote|eukaryotes]], including the incorporation of eukaryotic traits such as the incorporation of [[alphaproteobacteria]]l [[Mitochondrion|mitochondrial]] [[endosymbiont]]s.
Euglenozoa are a large group of [[flagellate]] [[Discoba]]. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. Euglenozoa are represented by four major classes, ''i.e.,'' [[Kinetoplastea]], [[Diplonemea]], [[Euglenid|Euglenida]], and Symbiontida. Euglenozoa are unicellular, mostly around {{convert|15–40|μm|abbr=on}} in size, although some euglenids get up to {{convert|500|μm|abbr=on}} long.<ref>{{cite web |title=Euglenozoa |url=https://eol.org/pages/4841/articles |website=Encyclopedia of Life |publisher=National Museum of Natural History - Smithsonian Institution |access-date=16 January 2020}}</ref><ref>{{Cite journal |last=Cavalier-Smith |first=Thomas |date=2016-10-01 |title=Higher classification and phylogeny of Euglenozoa |url=https://www.sciencedirect.com/science/article/pii/S0932473916300839 |journal=European Journal of Protistology |volume=56 |pages=250–276 |doi=10.1016/j.ejop.2016.09.003 |issn=0932-4739 |doi-access=free}}</ref>
==Characteristics== Euglenozoa are characterized by the ultrastructure of the [[Flagellum|flagella]]. In addition to the normal supporting microtubules or [[axoneme]], each contains a rod (called ''paraxonemal''), which has a tubular structure in one flagellum and a latticed structure in the other. Based on this, two smaller groups are included: the [[diplonemid]]s and ''[[Postgaardi]]''.<ref name="Sim1997">{{cite journal | vauthors = Simpson AG | title = The Identity and Composition of Euglenozoa | journal = Archiv für Protistenkunde | year = 1997 | volume = 148 | issue = 3 | pages = 318–328 | doi=10.1016/s0003-9365(97)80012-7}}</ref>
Symbiontida is a third deep-branching euglenozoan [[clade]] that may be a sister to Euglenoida but does not branch within them or [[Glycomonada]] on the evolutionary most realistic sequence trees presented in the next three sections, contrary to some poorly resolved earlier trees. They were placed in the new subphylum Postgaardia as class Postgaardea because they are radically different ultrastructurally from both euglenoids and glycomonads.<ref name="Cavalier-Smith" />
Symbiontida are [[biciliate]] free-living anaerobes covered in epibiotic bacteria in longitudinal rows are the diagnosis. A highly contractile pellicle with multiple evenly spaced microtubules and no morphogenetic pairs that are specifically distinguished. Without cytostomal or reservoir encircling fibers, cemented jaw supports, or hard longitudinal straight cemented rods, the [[cytopharynx]] is simplified. Symbiontida is the lone included class in etymology.<ref name="Cavalier-Smith" />
Reconstructions of FA ultrastructure in ''Postgaardi'' and ''[[Calkinsia]]'' confirmed that they were fundamentally similar and deserved to be classified together as a distinct order Postgaardida, as both genera share six finger-like projections.<ref name="Cavalier-Smith" />
==Taxonomy== According to Cavalier-Smith (2016):<ref name="Cavalier-Smith2">{{Cite journal |last=Cavalier-Smith |first=Thomas |date=2016-10-01 |title=Higher classification and phylogeny of Euglenozoa |url=https://www.sciencedirect.com/science/article/pii/S0932473916300839 |journal=European Journal of Protistology |volume=56 |pages=250–276 |doi=10.1016/j.ejop.2016.09.003 |issn=0932-4739 |doi-access=free}}</ref> * Subphylum '''Postgaardia''' <small>Cavalier-Smith 2016</small> ** Class '''Postgaardea''' <small>Cavalier-Smith 1998 s.s.</small> [Symbiontida <small>Yubuki et al., 2009</small>] *** Order [[Bihospitida]] <small>Cavalier-Smith 2016</small> **** Family [[Bihospitidae]] <small>Cavalier-Smith 2016</small> *** Order [[Postgaardida]] <small>Cavalier-Smith 2003</small> **** Family [[Calkinsiidae]] <small>Cavalier-Smith 2016</small> **** Family [[Postgaardidae]] <small>Cavalier-Smith 2016</small> According to Kostygov ''et al.'' (2023):<ref name="Kostygov-2023"/> * Class '''Symbiontida''' {{au|Yubuki, Edgcomb, Bernhard & Leander 2009}} **''[[Bihospites]]'' {{au|Breglia, Yubuki, Hoppenrath & Leander 2010}} **''[[Calkinsia]]'' {{au|Lackey 1960}} **''[[Postgaardi]]'' {{au|Fenschel, Bernard, Esteban, Findlay, Hansen & Iversen 1995}}
==References== {{Reflist}}
== External links == *[http://tolweb.org/Euglenozoa/2405 Tree of Life: Euglenozoa] {{Discoba}} {{Taxonbar|from1=Q31872919|from2=Q61996438|from3=Q6083465}}
[[Category:Euglenozoa classes]]
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