View source for Xenophyophorea

{{Short description|Clade of single-celled organisms}}
{{Automatic taxobox
| image = XenophyophoreNOAA.jpg
| image_alt = 
| image_caption = Image of a deep sea xenophyophore
| image2 = Xenophyophore.jpg
| image2_caption = Xenophyophore at the Galapagos Rift
| taxon = Xenophyophorea
| authority = [[Franz Eilhard Schulze|Schulze]], 1904
| synonyms = 
| synonyms_ref = 
| subdivision_ranks = Orders and subtaxa ''[[incertae sedis]]''<ref>Hayward, B.W.; Le Coze, F.; Gross, O. (2019). World Foraminifera Database. Monothalamea. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=744106 on 2019-01-07</ref>
| subdivision = *[[Psamminida]] <small>Poche, 1913</small>
*[[Stannomida]] <small>Tendal, 1972</small> 
*Clade incertae sedis
**[[Ammoclathrinidae]] <small>Tendal, 1972</small><ref>Tendal, O.S. (1972) A MONOGRAPH OF THE XENOPHYOPHORIA (Rhizopodea, Protozoa)</ref>
}}

'''Xenophyophorea''' {{IPAc-en|,|z|E|n|@|,|f|aI|@|'|f|oU|r|i:|@}} is a clade of [[foraminifera]]ns. Xenophyophores are [[multinucleate]] [[unicellular organism]]s found on the ocean floor throughout the world's [[ocean]]s, at depths of {{convert|500|to|10600|m|ft}}.<ref name="MSN-20111024">{{cite web |author=MSNBC Staff |title=Giant amoebas discovered in deepest ocean trench |url=https://www.nbcnews.com/id/wbna44998895 |date=22 October 2011 |publisher=[[NBC News]] |access-date=2011-10-24 |author-link=MSNBC }}</ref><ref name="Danish Science Press">{{cite book|title=A Monograph of the Xenophyophoria (Rhizopodea, Protozoa) (Doctoral dissertation)|date=1972|publisher=Danish Science Press|last1=Tendal|first1=O. S.}}</ref> They are a kind of [[foraminiferan]] that extract minerals from their surroundings and use them to form an exoskeleton known as a [[Test (biology)|test]].

They were first described by [[Henry Bowman Brady]] in 1883. They are abundant on [[abyssal plains]], and in some regions are the dominant species. Fifteen [[genus|genera]] and 75 [[species]] have been described, varying widely in size.<ref name=":0">{{Cite journal|last1=Gooday|first1=Andrew J.|last2=Holzmann|first2=Maria|last3=Goineau|first3=Aurélie|last4=Pearce|first4=Richard B.|last5=Voltski|first5=Ivan|last6=Weber|first6=Alexandra A.-T.|last7=Pawlowski|first7=Jan|date=2018-08-03|title=Five new species and two new genera of xenophyophores (Foraminifera: Rhizaria) from part of the abyssal equatorial Pacific licensed for polymetallic nodule exploration|url=https://academic.oup.com/zoolinnean/article/183/4/723/4757204|journal=Zoological Journal of the Linnean Society|language=en|volume=183|issue=4|pages=723–748|doi=10.1093/zoolinnean/zlx093|issn=0024-4082|doi-access=free}}</ref> The largest, ''[[Syringammina fragilissima]]'', is among the largest known [[coenocyte]]s, reaching up to {{convert|20|cm|0}} in diameter.<ref name="sciencedirect.com">{{cite journal |last1=Gooday |first1=A.J |last2=Aranda da Silva |first2=A. |last3=Pawlowski |first3=J. |title=Xenophyophores (Rhizaria, Foraminifera) from the Nazare Canyon (Portuguese margin, NE Atlantic) |journal=Deep-Sea Research Part II |date=2011 |volume=58 |issue=23–24 |pages=2401–2419 |doi=10.1016/j.dsr2.2011.04.005|bibcode=2011DSRII..58.2401G }}</ref>

== Naming and classification ==
The name Xenophyophora means "bearer of foreign bodies", from the [[Greek language |Greek]]. This refers to the sediments, called xenophyae, which are cemented together to construct their [[Test (biology) |tests]]. In 1883, [[Henry Bowman Brady]] classified them as primitive [[Foraminifera]].<ref>{{cite journal |last1=Brady |first1=H.B. |date=1884 |title=Report on the Foraminifera. Report on the Scientific Results of the Voyage of H. M. S. Challenger |volume=9 |pages=1–814}}</ref> Later they were placed within the [[sea sponge |sponges]].<ref>{{cite journal |last1=Haeckel |first1=E. |date=1889 |title=Report on the scientific results of the voyage of H. M. S. Challenger during the years 1873–76 |journal=Zoology |volume=32 |pages=1–92}}</ref> In the beginning of the 20th century they were considered an independent class of Rhizopoda,<ref>{{cite journal |last1=Schulze |first1=F. E. |date=1907 |title=Die Xenophyophoren, eine besondere Gruppe der Rhizopoden |journal=Wissenschaftliche Ergebnisse der Deutschen Tiefsee-Expedition Auf dem Dampfer 'Validivia' 1898–1899 |volume=11 |pages=1–55}}</ref> and later as a new eukaryotic phylum of [[Protist]]a.<ref>{{cite book |last1=Lee |first1=J. J. |title=The illustrated guide to the protozoa |last2=Leedale |first2=G. F. |last3=Bradbury |first3=P. |date=2000 |publisher=Society of protozoologists. Lawrence, KS: Allen Press |edition=2nd}}</ref> Phylogenetic studies suggest that xenophyophores are a specialized group of monothalamous (single-chambered) [[Foraminifera]].<ref>{{cite journal |last1=Pawlowski |first1=J. |last2=Holzmann |first2=M. |last3=Fahrni |first3=J. |last4=Richardson |first4=S.L. |date=2003 |title=Small subunit ribosomal DNA suggests that the xenophyophorean Syringammina corbicula isa Foraminiferan |url=https://www.scopus.com/record/display.url?eid=2-s2.0-0346965975&origin=inward&txGid=F4CB51D4D3484F134ACC334A40E7CEFF.aqHV0EoE4xlIF3hgVWgA%3a2 |journal=Journal of Eukaryotic Microbiology |volume=50 |issue=6 |pages=483–487 |doi=10.1111/j.1550-7408.2003.tb00275.x |pmid=14733441 |s2cid=39906626}}</ref><ref>{{Cite journal |last1=Lecroq |first1=Béatrice |last2=Gooday |first2=Andrew John |last3=Tsuchiya |first3=Masashi |last4=Pawlowski |first4=Jan |date=2009-07-01 |title=A new genus of xenophyophores (Foraminifera) from Japan Trench: morphological description, molecular phylogeny and elemental analysis |journal=Zoological Journal of the Linnean Society |volume=156 |issue=3 |pages=455–464 |doi=10.1111/j.1096-3642.2008.00493.x |issn=1096-3642 |doi-access=free}}</ref><ref>{{Cite journal |last1=Gooday |first1=A. J. |last2=Aranda da Silva |first2=A. |last3=Pawlowski |first3=J. |date=2011-12-01 |title=Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic) |journal=Deep-Sea Research Part II: Topical Studies in Oceanography |series=The Geology, Geochemistry, and Biology of Submarine Canyons West of Portugal |volume=58 |issue=23–24 |pages=2401–2419 |bibcode=2011DSRII..58.2401G |doi=10.1016/j.dsr2.2011.04.005}}</ref>

A 2013 molecular study using [[SSU rRNA |small subunit rDNA]] found ''[[Syringammina fragilissima |Syringammina]]'' and ''[[Shinkaiya]]'' to form a monophyletic clade closely related to ''[[Rhizammina |Rhizammina algaeformis]]''.<ref>{{Cite journal |last1=Pawlowski |first1=Jan |last2=Holzmann |first2=Maria |last3=Tyszka |first3=Jarosław |date=2013-04-01 |title=New supraordinal classification of Foraminifera: Molecules meet morphology |url=http://www.sciencedirect.com/science/article/pii/S0377839813000327 |journal=Marine Micropaleontology |language=en |volume=100 |pages=1–10 |bibcode=2013MarMP.100....1P |doi=10.1016/j.marmicro.2013.04.002 |issn=0377-8398}}</ref> Further molecular evidence has confirmed the [[monophyly]] of xenophyophores. This study also suggested that many individual genera are polyphyletic, with similar body shapes [[Convergent evolution |convergently evolving]] multiple times.<ref name=":1">{{Cite journal |last1=Gooday |first1=Andrew J |last2=Holzmann |first2=Maria |last3=Caulle |first3=Clémence |last4=Goineau |first4=Aurélie |last5=Kamenskaya |first5=Olga |last6=Weber |first6=Alexandra A. -T. |last7=Pawlowski |first7=Jan |date=2017-03-01 |title=Giant protists (xenophyophores, Foraminifera) are exceptionally diverse in parts of the abyssal eastern Pacific licensed for polymetallic nodule exploration |journal=Biological Conservation |language=en |volume=207 |pages=106–116 |doi=10.1016/j.biocon.2017.01.006 |issn=0006-3207 |doi-access=free}}</ref>

Historically xenophyophores have been divided into the agglutinated [[Psamminida]] and the flexible, proteinaceous [[Stannomida]].<ref name=":2" /> However, cladistic analyses based on molecular data have suggested a high amount of [[homoplasy]], and that the division between psamminids and stannomids is not well supported.<ref name=":1" />

==Anatomy==
[[File:Expl2234 - Flickr - NOAA Photo Library.jpg|left|thumb|A large 20-cm wide xenophyophore]]
Xenophyophores are unicellular, but have many [[Cell nucleus|nuclei]]. 
Many form delicate and elaborate agglutinated [[Test (biology)|tests]]—shells often made of calcium carbonate (CaCO<sub>3</sub>) and other foreign mineral particles glued together with organic cements<ref>{{Cite web|url=http://www.ucl.ac.uk/GeolSci/micropal/foram.html|title=Foraminifera|last=London|first=Postgraduate Unit of Micropalaeontology, University College|date=2002|website=www.ucl.ac.uk|language=en|access-date=2018-06-17}}</ref>—that range from a few millimetres to 20 centimetres across.  The softness and structure of tests varies from soft and lumpy shapes to fans and complex structures.

Some xenophyophores—notably ''[[Psammina]]''—have compartmentalized tests consisting of multiple chambers.<ref name=":2">{{Cite journal|last1=Antcliffe|first1=Jonathan B.|last2=Gooday|first2=Andrew J.|last3=Brasier|first3=Martin D.|date=2011|title=Testing the protozoan hypothesis for Ediacaran fossils: a developmental analysis of Palaeopascichnus|journal=Palaeontology|language=en|volume=54|issue=5|pages=1157–1175|doi=10.1111/j.1475-4983.2011.01058.x|issn=1475-4983|doi-access=free}}</ref>

Species of this group are morphologically variable, but the general structural pattern includes a test enclosing a branching system of organic tubules together with masses of waste material.

A number of unique terms are used to refer to anatomical aspects of the group:

* Individual waste pellets are referred to as ''stercomes'' or ''[[stercomata]]''; pellets that are bundled together in long strings are referred to as ''stercomares''.  Stercomares also include small, yellow-red spherical bodies known as ''xanthosomes''.
* Xenophyophores also commonly have abundant crystals of [[Baryte|barite]] called ''granellae'' within their cytoplasm. This is not to be confused with the ''granellare'', which refers to the plasma body and its tube.
* ''Linellae'' are long (several mm in length), threadlike structures found outside of the granellare in some xenophyophores (genera traditionally grouped together as "stannomida"); they are flexible and form part of the test.
* ''Xenophyae'', for which the group is named, are the agglutinated particles from which the test is constructed. They vary by species; they can contain sediment particles, sponge spicules, [[radiolaria]]n tests, and even the tests of smaller [[foraminifera]].<ref name="Danish Science Press" />

The [[protoplasm]] of xenophyophores contributes less than 1% of the total mass of the organism.<ref name=":3">{{Citation|last1=Levin|first1=L. A.|title=Possible Roles for Xenophyophores in Deep-Sea Carbon Cycling|date=1992|url=https://doi.org/10.1007/978-94-011-2452-2_6|work=Deep-Sea Food Chains and the Global Carbon Cycle|pages=93–104|editor-last=Rowe|editor-first=Gilbert T.|series=NATO ASI Series|place=Dordrecht|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-011-2452-2_6|isbn=978-94-011-2452-2|access-date=2020-09-30|last2=Gooday|first2=A. J.|editor2-last=Pariente|editor2-first=Vita}}</ref>

They select certain minerals and elements from their environment that are included in its tests and [[cytoplasm]], or concentrated in excretions. The selected minerals vary with species, but often include barite, lead and uranium.<ref>{{Cite journal|last1=Rothe|first1=N.|last2=Gooday|first2=A. J.|last3=Pearce|first3=R. B.|date=2011-12-01|title=Intracellular mineral grains in the xenophyophore Nazareammina tenera (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)|journal=Deep-Sea Research Part I: Oceanographic Research Papers|volume=58|issue=12|pages=1189–1195|doi=10.1016/j.dsr.2011.09.003|bibcode=2011DSRI...58.1189R}}</ref> The granellare of ''[[Shinkaiya]]'' have been found to contain high concentrations of [[Mercury (element)|mercury]].<ref>{{Cite journal|last1=Gooday|first1=Andrew J.|last2=Sykes|first2=Dan|last3=Góral|first3=Tomasz|last4=Zubkov|first4=Mikhail V.|last5=Glover|first5=Adrian G.|date=2018-08-14|title=Micro-CT 3D imaging reveals the internal structure of three abyssal xenophyophore species (Protista, Foraminifera) from the eastern equatorial Pacific Ocean|url= |journal=Scientific Reports|language=en|volume=8|issue=1|pages=12103|doi=10.1038/s41598-018-30186-2|pmid=30108286|pmc=6092355|bibcode=2018NatSR...812103G|issn=2045-2322}}</ref>

Studies have found unusually high concentrations of radioactive nuclides in xenophyophores; this was first reported in ''[[Occultammina]]'' but has since been found to be true of many other xenophyophore species from different parts of the ocean.<ref>{{Cite journal|last1=Swinbanks|first1=David D.|last2=Shirayama|first2=Yoshihisa|date=March 1986|title=High levels of natural radionuclides in a deep-sea infaunal xenophyophore|url=http://www.nature.com/articles/320354a0|journal=Nature|language=en|volume=320|issue=6060|pages=354–358|doi=10.1038/320354a0|bibcode=1986Natur.320..354S|s2cid=4254138|issn=0028-0836}}</ref><ref>{{Cite journal|last=Domanov|first=M. M.|date=July 2015|title=Natural 226Ra and 232Th radionuclides in xenophyophores of the Pacific Ocean|url=http://link.springer.com/10.1134/S0016702915070034|journal=Geochemistry International|language=en|volume=53|issue=7|pages=664–669|doi=10.1134/S0016702915070034|s2cid=127121951|issn=0016-7029}}</ref>

== Growth and reproduction ==
Very little is known about xenophyophore reproduction. It is assumed that an [[alternation of generations]] takes place, as in other [[foraminifera]]; however, this has not been confirmed.

Gametes form in a specialised part of the granellare that may look like swollen side-branch (in ''[[Psammetta]]'') or a stalked bulb (in ''[[Cerelasma]]''). Gametes are reportedly about 20&nbsp;μm in diameter, with two flagella; after this, an amoeba-like stage seems to be present. It is also possible that the amoeboid stage represents amoeboid gametes, found in other foraminifera. These amoeboid structures are also sometimes found inside the granellare. Juveniles have occasionally been found in association with adults; in Psametta they are horseshoe-shaped and already covered in xenophyae.

The location of the initial plasma can sometimes be pointed out in adult xenophyophores. In some species this is denoted by a sharp change in the type of xenophyae; in others, the juvenile is regular and the adult is irregular; still others flip this pattern, so that the juvenile is irregular and the adult is regular.<ref name="Danish Science Press" />

Growth is episodic; one observational study taking place over a period of eight months saw a three-to-tenfold growth in specimens of [[Reticulammina|''Reticulammina labyrinthica'']]. This growth occurred in phases lasting 2–3 days each; each phase was separated by a resting period of approximately two months. These growth phases were approximately synchronous between specimens, but it is unclear if this is biologically or developmentally controlled; some evidence suggests the synchrony may have been due to chance.

Each episode of growth occurred in three phases: first, the base becomes wider and flatter, causing the surface texture to become smoother; then, the original shape of the organism is regained (albeit larger); and finally, the surface texture is rebuilt. The rapid rate of growth observed suggests that xenophyophores may not be as long-lived as previously hypothesised.<ref>{{Cite journal|last1=Gooday|first1=A.J.|last2=Bett|first2=B.J.|last3=Pratt|first3=D.N.|date=November 1993|title=Direct observation of episodic growth in an abyssal xenophyophore (Protista)|url=https://linkinghub.elsevier.com/retrieve/pii/096706379390094J|journal=Deep Sea Research Part I: Oceanographic Research Papers|language=en|volume=40|issue=11–12|pages=2131–2143|doi=10.1016/0967-0637(93)90094-J|bibcode=1993DSRI...40.2131G}}</ref>[[File:Occultammina sp.png|left|thumb|''[[Occultammina]]'' sp. from the Porcupine Abyssal Plain in the NE Atlantic, from a depth of about 4800m.]]

== Habitat and range ==
Xenophyophores are an important part of the deep sea-floor, as they have been found in all four major ocean basins.<ref name="Danish Science Press" /><ref name="Kluwer Academic">{{cite book|last1=Levin|first1=L. A.|title=Possible roles for Xenophyophores in dee-sea carbon cycling. In: Deep-Sea Food Chains and the Global Carbon Cycle|last2=Gooday|first2=A. J.|date=1992|publisher=Kluwer Academic|editor1-last=Rowe|editor1-first=G. T.|location=The Netherlands|pages=93–104|editor2-last=Pariente|editor2-first=V.}}</ref><ref>{{cite journal|last1=Levin|first1=L. A|date=1991|title=Interactions between metazoans and large, agglutinating protozoans: implications for the community structure of deep-sea benthos|journal=American Zoologist|volume=31|issue=6|pages=886–900|doi=10.1093/icb/31.6.886|doi-access=free}}</ref><ref>{{cite journal|last1=Tendal|first1=O. S.|date=1996|title=Synoptic checklist and bibliography of the Xenophyophorea (Protista), with a zoogeopgraphical survey of the group|url=http://www.zmuc.dk/inverweb/galathea/Pdf_filer/Volume_17/galathea-vol.17-pp_079-102.pdf|journal=Galathea Report|volume=17|pages=79–101}}</ref> They are often found in areas of enhanced organic carbon flux, such as beneath productive surface waters, in sub-marine canyons, in settings with sloped topography (e.g. seamounts, abyssal hills) and on continental slopes.<ref name="Danish Science Press" /><ref name="sciencedirect.com" /><ref>{{cite journal|last1=Tendal|first1=O. S.|last2=Gooday|first2=A. J.|date=1981|title=Xenophyophoria (Rhizopoda, Protozoa) in bottom photographs from the bathyal and abyssal NE Atlantic|url=http://archimer.ifremer.fr/doc/00121/23226/21060.pdf|journal=Oceanologica Acta|volume=4|pages=415–422}}</ref><ref>{{cite journal|last1=Levin|first1=L. A.|last2=DeMaster|first2=D. J.|last3=McCann|first3=L. D.|last4=Thomas|first4=C. L.|date=1986|title=Effect of giant protozoans (class: Xenophyophorea) on deep-seamount benthos|journal=Marine Ecology Progress Series|volume=29|pages=99–104|bibcode=1986MEPS...29...99L|doi=10.3354/meps029099|doi-access=free}}</ref> They are not found in areas of [[Hypoxic zone|hypoxic]] waters.<ref name=":3" />

Xenophyophores have been found between depths of 500 and 10,600 metres. Most are epifaunal (living atop the seabed), but one species (''[[Occultammina|Occultammina profunda]]''), is known to be infaunal; it buries itself up to {{convert|6|cm}} deep into the sediment.<ref name="MSN-20111024" /><ref name="Danish Science Press" /><ref>{{Cite journal|last1=Tendal|first1=Os|last2=Swinbanks|first2=Dd|last3=Shirayama|first3=Y.|date=1982-01-01|title=A new infaunal xenophyophore (xenophyophorea, protozoa) with notes on its ecology and possible trace fossil analogs|url=https://archimer.ifremer.fr/doc/00120/23170/|journal=Oceanologica Acta|language=en|volume=5|issue=3|pages=325–329|issn=0399-1784}}</ref>

Xenophyophore densities are highest on soft sediments; however, they may still be found on rocky substrates including [[basalt]]s, canyon walls, and [[Manganese nodule|manganese]] crusts.<ref name=":3" />

==Feeding==
The diet and feeding ecology of xenophyophores was long the subject of speculation; the fragile tests and deepwater habitat of the group makes ''in vivo'' observation difficult. Early propositions included [[suspension feeding]], bacterial farming, deposit feeding, and trapping particulate matter inside the test.<ref name=":3" /> Studies have since confirmed active uptake of food from surrounding sediments using the [[pseudopodia]] and using the test to trap particles. Analysis of lipid concentrations within xenophyophores revealed especially high concentrations of bacteria in the stercomata, suggesting that xenophyophores utilise bacteria growing on their waste products in order to supplement their feeding.<ref>{{Cite journal|last1=Laureillard|first1=J|last2=Méjanelle|first2=L|last3=Sibuet|first3=M|date=2004|title=Use of lipids to study the trophic ecology of deep-sea xenophyophores|url=https://www.int-res.com/abstracts/meps/v270/p129-140/|journal=Marine Ecology Progress Series|language=en|volume=270|pages=129–140|doi=10.3354/meps270129|bibcode=2004MEPS..270..129L|issn=0171-8630|doi-access=free}}</ref>

A 2021 study that utilised [[isotopic labeling]] to examine the question of xenophyophore feeding confirmed rapid uptake of both [[diatom]]s and [[Dissolved organic carbon|dissolved organic matter]] in the form of [[glucose]]. This study found no evidence to support a bacterial farming function for the test, and instead proposed that it aided to function in the collection of [[phytodetritus]] by increasing surface area. These authors argued that xenophyophores fill a major role in ocean-floor [[Biogeochemical cycle|biogeochemical cycling]].<ref>{{Cite journal|last1=Tsuchiya|first1=Masashi|last2=Nomaki|first2=Hidetaka|date=2021-10-01|title=Rapid response of the giant protist xenophyophores (Foraminifera, Rhizaria) to organic matter supply at abyssal depths revealed by an in situ dual stable isotope labeling experiment|url=https://www.sciencedirect.com/science/article/pii/S0967063721001473|journal=Deep Sea Research Part I: Oceanographic Research Papers|language=en|volume=176|pages=103608|doi=10.1016/j.dsr.2021.103608|bibcode=2021DSRI..17603608T |issn=0967-0637}}</ref>

== Fossil record ==
As of 2017, no positively-identified xenophyophore fossils had been discovered.<ref name=":1"/>
[[File:Paleodictyon P.San García Algeciras I03.JPG|thumb|''[[Paleodictyon]]'' has been suggested as a fossil xenophyophore, but this remains controversial.]]
It has been suggested that the mysterious [[vendozoa]]ns of the [[Ediacaran]] period represent fossil xenophyophores.<ref>{{Cite journal|last=Seilacher|first=A.|date=2007-01-01|title=The nature of vendobionts|url=https://sp.lyellcollection.org/content/286/1/387|journal=Geological Society, London, Special Publications|language=en|volume=286|issue=1|pages=387–397|doi=10.1144/SP286.28|bibcode=2007GSLSP.286..387S|s2cid=128619251|issn=0305-8719}}</ref> However, the discovery of C<sub>27</sub> [[sterol]]s associated with the fossils of ''[[Dickinsonia]]'' cast doubt on this identification, as these sterols are today associated only with animals. These researchers suggest that ''Dickinsonia'' and relatives are instead [[Stem-group|stem]]-[[bilateria]]ns.<ref>{{Cite journal|last1=Bobrovskiy|first1=Ilya|last2=Hope|first2=Janet M.|last3=Ivantsov|first3=Andrey|last4=Nettersheim|first4=Benjamin J.|last5=Hallmann|first5=Christian|last6=Brocks|first6=Jochen J.|date=2018-09-21|title=Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals|journal=Science|language=en|volume=361|issue=6408|pages=1246–1249|doi=10.1126/science.aat7228|issn=0036-8075|pmid=30237355|bibcode=2018Sci...361.1246B|doi-access=free|hdl=1885/230014|hdl-access=free}}</ref> Other ediacaran fossils, such as ''[[Palaeopascichnus]]'' ''[[Intrites]]'', ''[[Yelovichnus]]'', and ''[[Neonereites]]'' have been posited as fossil xenophyophores and linked to the Eocene fossil ''[[Benkovacina]].'' However, analysis of the latter found neither barite crystals nor evidence of agglutinated foraminifera in the wall.<ref>{{Cite journal|last1=Seilacher|first1=Adolf|last2=Grazhdankin|first2=Dmitri|last3=Legouta|first3=Anton|date=2003-03-31|title=Ediacaran biota: The dawn of animal life in the shadow of giant protists|journal=Paleontological Research|language=en|volume=7|issue=1|pages=43–54|doi=10.2517/prpsj.7.43|s2cid=85146476|issn=1342-8144|doi-access=free}}</ref><ref>{{Cite journal|last1=Seilacher|first1=Adolf|last2=Mrinjek|first2=Erwin|date=December 2011|title=Benkovac Stone (Eocene, Croatia): a deep-sea Plattenkalk?|url=http://link.springer.com/10.1007/s00015-011-0051-7|journal=[[Swiss Journal of Geosciences]]|language=en|volume=104|issue=S1|pages=159–166|doi=10.1007/s00015-011-0051-7|s2cid=128952011|issn=1661-8726|doi-access=free}}</ref>  A 2011 study that examined growth and development of ''Palaeopascichnus'' concluded it was likely not a xenophyophore.<ref name=":2" /> A 2014 study of ''[[Pteridinium|Pteridinum]]'' reached similar conclusions.<ref>{{Cite journal|last1=Meyer|first1=Mike|last2=Elliott|first2=David|last3=Wood|first3=Andrew D.|last4=Polys|first4=Nicholas F.|last5=Colbert|first5=Matthew|last6=Maisano|first6=Jessica A.|last7=Vickers-Rich|first7=Patricia|last8=Hall|first8=Michael|last9=Hoffman|first9=Karl H.|last10=Schneider|first10=Gabi|last11=Xiao|first11=Shuhai|date=2014-08-01|title=Three-dimensional microCT analysis of the Ediacara fossil Pteridinium simplex sheds new light on its ecology and phylogenetic affinity|url=http://www.sciencedirect.com/science/article/pii/S0301926814001429|journal=Precambrian Research|language=en|volume=249|pages=79–87|doi=10.1016/j.precamres.2014.04.013|bibcode=2014PreR..249...79M|issn=0301-9268}}</ref>

Some researchers have suggested that the enigmatic [[Graphoglyptidae|graphoglyptids]] ''[[Paleodictyon]]'', known from the early [[Cambrian]] through recent times, could represent the remains of xenophyophores,<ref>{{Cite journal|last=Jensen|first=Soren|title=Jensen, S. and Palacios, T. 2006. A peri-Gondwanan cradle for the trace fossil Paleodictyon. In: 22 Jornadas de Paleontologia, Comunicaciones, 132-134|url=https://www.academia.edu/890535|language=en}}</ref><ref>{{Cite journal|last=Swinbanks|first=D. D.|date=1982-10-01|title=Piaeodicton: The Traces of Infaunal Xenophyophores?|url=https://www.science.org/doi/10.1126/science.218.4567.47|journal=Science|language=en|volume=218|issue=4567|pages=47–49|doi=10.1126/science.218.4567.47|issn=0036-8075|pmid=17776707|bibcode=1982Sci...218...47S|s2cid=28690086}}</ref> and noted the similarity of the extant xenophyophore ''[[Occultammina]]'' to the fossil.<ref name=":8">{{Cite journal|last=Levin|first=Lisa A.|date=1994|title=Paleoecology and Ecology of Xenophyophores|journal=PALAIOS|volume=9|issue=1|pages=32–41|doi=10.2307/3515076|jstor=3515076|bibcode=1994Palai...9...32L|issn=0883-1351}}</ref> Supporting this notion is the similar abyssal habitat of living xenophyophores to the inferred habitat of fossil graphoglyptids; however, the large size (up to 0.5m) and regularity of many graphoglyptids as well as the apparent absence of xenophyae in their fossils casts doubt on the possibility.<ref name=":8" /> Modern examples of ''Paleodictyon'' have been discovered; however, no evidence of tests, stercomares, grannelares, or xenophyophore DNA was found, and the trace may alternately represent a burrow or a [[Hexactinellid|glass sponge.]]<ref>{{Cite journal|last1=Rona|first1=Peter A.|last2=Seilacher|first2=Adolf|last3=de Vargas|first3=Colomban|last4=Gooday|first4=Andrew J.|last5=Bernhard|first5=Joan M.|last6=Bowser|first6=Sam|last7=Vetriani|first7=Costantino|last8=Wirsen|first8=Carl O.|last9=Mullineaux|first9=Lauren|last10=Sherrell|first10=Robert|last11=Frederick Grassle|first11=J.|date=2009-09-01|title=Paleodictyon nodosum: A living fossil on the deep-sea floor|url=http://www.sciencedirect.com/science/article/pii/S0967064509001799|journal=Deep Sea Research Part II: Topical Studies in Oceanography|series=Marine Benthic Ecology and Biodiversity: A Compilation of Recent Advances in Honor of J. Frederick Grassle|language=en|volume=56|issue=19|pages=1700–1712|doi=10.1016/j.dsr2.2009.05.015|bibcode=2009DSRII..56.1700R|issn=0967-0645}}</ref>

Certain [[Carboniferous]] fossils have been suggested to represent the remains of xenophyophores due to the concentration of [[barium]] within the fossils as well as supposed morphological similarity; however, the barium content was later determined to be due to [[Diagenesis|diagenetic]] alteration of the material and the morphology of the specimen instead supported an algal affinity.<ref>{{Cite journal|last=Torres|first=Andrew M.|date=1996|title=Fossil algae were very different from xenophyophores|journal=Lethaia|language=en|volume=29|issue=3|pages=287–288|doi=10.1111/j.1502-3931.1996.tb01661.x|issn=1502-3931}}</ref>

==Ecology==
[[File:Expl0011 - Flickr - NOAA Photo Library.jpg|thumb|270x270px|A deep sea community of organisms, including several xenophyophores; the two large individuals in the bottom middle have [[brittle star]]s on top.]]
Local population densities may be as high as 2,000 individuals per {{convert|100|m2}}, making them dominant organisms in some areas. Xenophyophores have been found to be "[[ecosystem engineer]]s", providing habitat and serving as traps for organic particles, increasing diversity in the surrounding area.<ref name=":4">{{Cite journal|last1=Ashford|first1=Oliver S.|last2=Davies|first2=Andrew J.|last3=Jones|first3=Daniel O.B.|date=December 2014|title=Deep-sea benthic megafaunal habitat suitability modelling: A global-scale maximum entropy model for xenophyophores|url=https://linkinghub.elsevier.com/retrieve/pii/S0967063714001411|journal=Deep Sea Research Part I: Oceanographic Research Papers|language=en|volume=94|pages=31–44|doi=10.1016/j.dsr.2014.07.012|bibcode=2014DSRI...94...31A}}</ref> Research has shown that areas dominated by xenophyophores have 3–4 times the number of benthic [[crustacea]]ns, [[echinoderm]]s, and [[mollusc]]s than equivalent areas that lack xenophyophores. The xenophyophores themselves also play [[commensalism|commensal]] host to a number of organisms&mdash;such as [[isopods]] (e.g., genus ''[[Hebefustis]]''), [[sipuncula]]n and [[polychaete]] worms, [[nematode]]s, and [[Harpacticoida|harpacticoid]] [[copepod]]s&mdash;some of which may take up semi-permanent residence within a xenophyophore's test. [[Brittle star]]s (Ophiuroidea) also appear to have a relationship with xenophyophores, as they are consistently found directly underneath or on top of the protozoans. They can also function as nurseries for fish; [[snailfish]] have been found to lay eggs in the shelter of the xenophyophore test.<ref>{{Cite journal|last1=Levin|first1=Lisa A.|last2=Rouse|first2=Greg W.|date=2020|title=Giant protists (xenophyophores) function as fish nurseries|url= |journal=Ecology|language=en|volume=101|issue=4|pages=e02933|doi=10.1002/ecy.2933|issn=1939-9170|pmc=7341444|pmid=31742677}}</ref>

[[Starfish]], [[monoplacophora]]ns, and [[Molpadiidae|molpadiid]] sea cucumbers have all been observed feeding on xenophyophores; specifically, the monoplacophoran ''[[Neopilina galatheae]]'' has been proposed as a specialised predator of the group.<ref name=":3" />

Despite this abundance, the relatively low amount of protoplasm per unit of test means that xenophyophores often contribute little to total biomass.<ref name=":3" />

Xenophyophores are difficult to study due to their extreme fragility. Specimens are invariably damaged during sampling, rendering them useless for captive study or [[cell culture]]. For this reason, very little is known of their [[Biological life cycle|life history]]. As they occur in all the world's oceans and in great numbers, xenophyophores could be indispensable agents in the process of sediment deposition and in maintaining [[biological diversity]] in benthic ecosystems.

Scientists in the submersible [[DSV Alvin]] at a depth of 3,088 metres at the Alaskan [[continental margin]] in the [[Gulf of Alaska]] collected a [[spatangoid|spatangoid urchin]], ''Cystochinus loveni'', about 5&nbsp;cm diameter, which was wearing a cloak consisting of over 1,000 protists and other creatures, including 245 living xenophyophores, mainly ''Psammina'' species, each 3–6&nbsp;mm. The fragility of the xenophyophores suggests that the urchin either very carefully collected them, or that they settled and grew there. Among several possible explanations for the urchin's behaviour, perhaps the most likely are chemical camouflage and weighing itself down to avoid being moved in currents.<ref>{{cite journal|last1=Levin|first1=Lisa A.|last2=Gooday|first2=Andrew J.|last3=James|first3=David W.|title=Dressing up for the deep: agglutinated protists adorn an irregular urchin|journal=Journal of the Marine Biological Association of the UK|volume=81|issue=5|year=2001|pages=881|issn=0025-3154|doi=10.1017/S0025315401004738|s2cid=86707195}}</ref>

Different xenophyophore ecomorphs are found in different settings; reticulated or heavily folded genera such as ''[[Reticulammina]]'' and ''[[Syringammina]]'' are more common in areas where the substrate is sloped or near canyon walls, while more fan-shaped forms like ''[[Stannophyllum]]'' are more common in areas with quieter water and/or lower primary productivity.<ref name=":3" />

== List of genera ==
{{Incomplete list|date=September 2020}}

* ''[[Syringammina]]''<ref name=":1" />
* ''[[Occultammina]]''<ref name=":1" />
* ''[[Aschemonella]]''<ref name=":1" />
* ''[[Psammina]]''<ref name=":1" />
* ''[[Galatheammina]]''<ref name=":1" />
* ''[[Semipsammina]]''<ref name=":1" />
* ''[[Stannophyllum]]''<ref name=":1" />
* ''[[Semipsammina]]''<ref name=":1" />
* ''[[Homogammina]]''<ref name=":1" />
* ''[[Rhizammina]]''<ref name=":1" />
* ''[[Shinkaiya]]''<ref name=":1" />
* ''[[Cerelasma]]''<ref name=":1" />
* ''[[Spiculammina]]''<ref name=":1" />
* ''[[Bizarria]]''<ref name=":0" />
* ''[[Tendalia]]''<ref name=":0" />
* ''[[Nazareammina]]''<ref>{{Cite journal|last1=Rothe|first1=N.|last2=Gooday|first2=A. J.|last3=Pearce|first3=R. B.|date=2011-12-01|title=Intracellular mineral grains in the xenophyophore Nazareammina tenera (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)|url=http://www.sciencedirect.com/science/article/pii/S0967063711001695|journal=Deep Sea Research Part I: Oceanographic Research Papers|language=en|volume=58|issue=12|pages=1189–1195|doi=10.1016/j.dsr.2011.09.003|bibcode=2011DSRI...58.1189R|issn=0967-0637}}</ref>
* ''[[Cerelpemma]]''<ref name=":1" />
* ''[[Maudammina]]''<ref name=":1" />
* ''[[Psametta]]''<ref name=":1" />
* ''[[Stannoma]]''<ref name=":1" />
* ''[[Maudammina]]''<ref name="Danish Science Press" />
* ''[[Cerelpemma]]''?<ref name="Danish Science Press" />
* ''[[Holopsamma]]''<ref name=":4" />
* ''[[Abyssalia]]''<ref name=":5">{{Cite journal|date=2020-08-01|title=Xenophyophores (Rhizaria, Foraminifera), including four new species and two new genera, from the western Clarion-Clipperton Zone (abyssal equatorial Pacific)|journal=European Journal of Protistology|language=en|volume=75|pages=125715|doi=10.1016/j.ejop.2020.125715|issn=0932-4739|last1=Gooday|first1=Andrew J.|last2=Durden|first2=Jennifer M.|last3=Holzmann|first3=Maria|last4=Pawlowski|first4=Jan|last5=Smith|first5=Craig R.|pmid=32585572|doi-access=free}}</ref>
* ''[[Moanammina]]''<ref name=":5" />

== See also ==
* [[Coenocyte]]
* [[Extremophile]]
* [[Piezophile]]

== References ==
{{Reflist|30em}}

==Further reading==
*Gubbay, S., Baker, M., Bettn, B., Konnecker, G. (2002). [https://web.archive.org/web/20050517164034/http://ngo.grida.no/wwfneap/Projects/Reports/Offshore.pdf "The offshore directory: Review of a selection of habitats, communities and species of the north-east Atlantic"], pp.&nbsp;74–77. 
*[[National Oceanic and Atmospheric Administration|NOAA]] Ocean Explorer. [https://web.archive.org/web/20051227112128/http://oceanexplorer.noaa.gov/explorations/03windows/background/education/media/03win_giants.pdf "Windows to the deep exploration: Giants of the protozoa"], p.&nbsp;2.

== External links ==
*[http://www.microscopy-uk.org.uk/mag/artnov98/xeno1.html Microscopy-UK: Note on Xenophyophores]
*[https://web.archive.org/web/20031024195414/http://www.soc.soton.ac.uk/GDD/DEEPSEAS/giantprotozoans.html More xenophyophore photos, with a map of their habitat]

{{Portal bar|Marine life|Biology}}

{{Rhizaria}}
{{Taxonbar|from1=Q632686|from2=Q16608712}}

[[Category:Foraminifera classes]]
[[Category:Monothalamea| ]]
[[Category:Extremophiles]]