{{Short description|Group of amoebae closely related to fungi}} {{good article}} {{Automatic taxobox | name = Nucleariids | image = Nuclearia sp Nikko.jpg | image_caption = ''Nuclearia thermophila'' | taxon = Nucleariidae | authority = Cann & Page 1979<ref name="Cann-1979"/> | parent_authority = Rainer 1968<ref name="Rainer-1968"/><ref name="Adl-2019"/> | display_parents = 6 | subdivision_ranks = Genera | subdivision = See text | diversity = Around 50 species<ref name="Gabaldón-2022"/> | synonyms_ref = <ref name="Adl-2019"/> | synonyms = * Cristidiscoidida {{au|Page 1987}}<ref name="Page-1987"/> * Cristidiscoidia {{au|Cavalier-Smith 1993}}<ref name="Cavalier-Smith-1993"/> * Pompholyxophryidae {{au|Page 1987}} * Nucleariae {{au|Tedersoo et al. 2018}}<ref name="Tedersoo-2018"/> * Nuclearida {{au|Tedersoo et al. 2018}} * Nuclearidea {{au|Tedersoo et al. 2018}} * Nucleariida {{au|Cavalier-Smith 1993}} * Fonticulida {{au|Tedersoo et al. 2018}} * Fonticulea {{au|Tedersoo et al. 2018}} * Fonticulida {{au|Cavalier-Smith 1993}} * Fonticulaceae {{au|Worley, Raper & Hohl 1979}}<ref name="Worley-1979"/> }}
The '''nucleariids''', or '''nucleariid amoebae''', are a group of amoebae that comprise the sister clade of the fungi. Together, they form the clade Holomycota. They are aquatic organisms found in freshwater and marine habitats, as well as in faeces. They are free-living phagotrophic predators that mostly consume algae and bacteria.
Nucleariids are characterized by simple, spherical or flattened single-celled bodies with filopodia (fine, thread-like pseudopods), covered by a mucous coat. They lack flagella and microtubules. Inside the cytoplasm of some species are endosymbiotic proteobacteria. Some species are naked, with only the mucous coat as cover, while others (known as 'scaled' nucleariids) have silica-based or exogenous particles of various shapes.
An exceptional nucleariid, ''Fonticula alba'', develops multicellular fruiting bodies (sorocarps) for spore dispersal. It is one of several cases of independently evolved multicellularity within Opisthokonta, the clade that houses both Holozoa (which includes animals) and Holomycota.
Initially, nucleariids were grouped with other filose amoebae (i.e., with filopodia) based on their superficial similarity. Silica-scaled and naked nucleariids were classified into separate families from one another, '''Pompholyxophryidae''' and '''Nucleariidae''', respectively. Due to its nature as a slime mold, the genus ''Fonticula'' has also been classified separatedly, particularly with acrasids and other slime molds. With advancements in electron microscopy and molecular phylogenetics, the three groups were revealed to belong to the same clade as sister to the fungi. Due to lack of molecular data, the three groups are treated as one family, under the name of Nucleariidae.
Various conflicting systems of above-family classification exist for nucleariids, with older systems grouping them as a class '''Cristidiscoidea''' composed of two orders: one for ''Fonticula'' and another for the remaining species. Mycologists regard them as an independent kingdom of life, '''Nucleariae''', with two phyla that mirror those two orders. They are generally accepted by protistologists as a single order '''Rotosphaerida''', which is the oldest taxonomic name for these organisms.
== Description ==
Nucleariids are single-celled amoebae that lack flagella and have radiating filopodia (i.e., thread-like pseudopodia). They have a spherical or sometimes flattened cell bodies<ref name="Zettler-2005"/> with one or few conspicuous nuclei, each with a prominent central nucleolus except for ''Fonticula'' and ''Parvularia'': ''Parvularia'' can also have peripheral nucleoral material instead,<ref name="López-Escardó-2017"/> and ''Fonticula'' has an indistinct nucleolus. The cytoplasm contains multiple vacuoles, including food vesicles, contractile vacuoles in freshwater species, and lipid globules. They have relatively simple cells in comparison to other protists: they lack flagella, cytoplasmic microtubules,{{efn|The putative nucleariid genus ''Vampyrellidium'' has cytoplasmic microtubules, but the remaining ultrastructural traits have supported its placement among nucleariids.<ref name="Gabaldón-2022"/>}} extrusomes, and special organelles.<ref name="Gabaldón-2022"/> Exceptionally, some species contain endosymbiotic proteobacteria (most frequently members of the genus ''Rickettsia'').<ref name="Galindo-2019"/>
Most nucleariids have some kind of mucous coat, with or without coverings. The coverings can be made with endogenous silica-based particles (known as idiosomes) or with exogenous particles (known as xenosomes).<ref name="Gabaldón-2022"/> These particles are developed into hollow siliceous scales or spines.<ref>{{cite journal |vauthors=Patterson DJ |title=On the Organization and Affinities of the Amoeba, ''Pompholyxophrys punicea'' Archer, Based on Ultrastructural Examination of Individual Cells from Wild Material 1 |journal=J. Protozool. |volume=32 |issue=2 |pages=241–6 |date=May 1985 |doi=10.1111/j.1550-7408.1985.tb03044.x }}</ref> The mucous coat itself—sometimes called glycocalyx—is enigmatic, as it can be present or absent in the same organism depending on the conditions. It appears to be made of one or two layers fibrous material running parallel to the cell membrane, and it often houses bacterial ectosymbionts. Surrounding the cell periphery, the characteristic hyaline (i.e., transparent) filopodia are found, originating from any point of the cell surface, sometimes branching or tapering but are never stiff or anastomosing (fusing with one another). Unlike Heliozoa, these filopodia are not supported by microtubules and do not contain extrusomes.<ref name="Gabaldón-2022"/>
Most species develop a resting cyst during their life cycle consisting of a smooth spherical cell covered by one or more thick layers of a translucent material.<ref name="Gabaldón-2022"/>
== Ecology ==
Nucleariids thrive in water bodies worldwide. Most live in a variety of freshwater environments, including hot spring waters of around 30 °C.<ref>{{cite journal |vauthors=Yoshida M, Nakayama T, Inouye I |title=Nuclearia thermophila sp. nov. (Nucleariidae), a new nucleariid species isolated from Yunoko Lake in Nikko (Japan) |journal=European Journal of Protistology |volume=45 |issue=2 |pages=147–155 |date=January 2009 |pmid=19157810 |doi=10.1016/j.ejop.2008.09.004 }}</ref> Others are found in marine environments (e.g., ''Lithocolla''), and others inhabit faeces (''Fonticula'').<ref name="Gabaldón-2022"/>
Nucleariids are free-living phagotrophs, and preferably consume cyanobacteria and other algae.<ref name="Zettler-2005">{{cite journal|title=The nucleariid amoebae: more protists at the animal-fungal boundary|first1=Linda A. Amaral|last1=Zettler|first2=Thomas A.|last2=Nerad|first3=Charles J.|last3=O'Kelly|first4=Mitchell L.|last4=Sogin|journal=Journal of Eukaryotic Microbiology|date=11 July 2005|issue=3|pmid=11411837|volume=48|doi=10.1111/j.1550-7408.2001.tb00317.x|pages=293–297|s2cid=44548329}}</ref> Small-celled species like those of ''Parvularia'' and ''Fonticula'' feed on small bacteria, while larger cells such as ''Nuclearia'', ''Pompholyxophrys'' and ''Lithocolla'' can also feed on detritus and unicellular eukaryotic algae (e.g., diatoms). All of them are slow-paced grazers<ref>{{cite journal|first1=Sebastian|last1=Dirren|first2=Gianna|last2=Pitsch|first3=Marisa O.D.|last3=Silva|first4=Thomas|last4=Posch|title=Grazing of ''Nuclearia thermophila'' and ''Nuclearia delicatula'' (Nucleariidae, Opisthokonta) on the toxic cyanobacterium ''Planktothrix rubescens''|journal=European Journal of Protistology|volume=60|date=August 2017|pages=87–101|doi=10.1016/j.ejop.2017.05.009|pmid=28675820 |url=https://www.zora.uzh.ch/id/eprint/144930/1/Dirren_2017_EJP.pdf }}</ref> that probably grow in response to the availability of their food sources, such as after algal blooms.<ref name="Gabaldón-2022"/>
== Evolution == [[File:Macro_photograph_of_an_F._alba_colony_radius_growing_on_a_plate.jpg|thumb|The nucleariid ''Fonticula alba'' developing into sorocarps. Scale bar: 1 mm.]] Nucleariids are among the closest relatives of fungi,<ref name="Steenkamp-2005">{{cite journal|last1=Steenkamp|first1=Emma T.|last2=Wright|first2=Jane|last3=Baldauf|first3=Sandra L.|date=8 September 2005|title=The Protistan Origins of Animals and Fungi|journal=Molecular Biology and Evolution|volume=23|issue=1|pages=93–106|doi=10.1093/molbev/msj011|pmid=16151185|doi-access=free}}</ref> together forming the clade Holomycota.<ref name="Brown-2009">{{Cite journal|last1=Brown|first1=Matthew W.|last2=Spiegel|first2=Frederick W.|last3=Silberman|first3=Jeffrey D.|date=2009-12-01|title=Phylogeny of the "Forgotten" Cellular Slime Mold, ''Fonticula alba'', Reveals a Key Evolutionary Branch within Opisthokonta|journal=Molecular Biology and Evolution|language=en|volume=26|issue=12|pages=2699–2709|doi=10.1093/molbev/msp185|issn=0737-4038|pmid=19692665|doi-access=free}}</ref><ref name="Liu-2009">{{cite journal|last1=Liu|first1=Yu|last2=Steenkamp|first2=Emma T.|last3=Brinkmann|first3=Henner|last4=Forget|first4=Lisa|first5=Hervé|last5=Philippe|first6=B. Franz|last6=Lang|title=Phylogenomic analyses predict sistergroup relationship of nucleariids and Fungi and paraphyly of zygomycetes with significant support|journal=BMC Evolutionary Biology|volume=9|page=272|date=2009|issue=1 |doi=10.1186/1471-2148-9-272|doi-access=free|pmc=2789072|pmid=19939264|bibcode=2009BMCEE...9..272L }}</ref><ref name="Tedersoo-2018">{{Cite journal|last1=Tedersoo|first1=Leho|last2=Sánchez-Ramírez|first2=Santiago|last3=Kõljalg|first3=Urmas|last4=Bahram|first4=Mohammad|last5=Döring|first5=Markus|last6=Schigel|first6=Dmitry|last7=May|first7=Tom|last8=Ryberg|first8=Martin|last9=Abarenkov|first9=Kessy|date=2018|title=High-level classification of the Fungi and a tool for evolutionary ecological analyses|journal=Fungal Diversity|language=en|volume=90|issue=1|pages=135–159|doi=10.1007/s13225-018-0401-0|issn=1560-2745|doi-access=free|hdl=10138/238983|hdl-access=free}}</ref><ref name="Gabaldón-2022">{{cite journal|first1=Toni|last1=Gabaldón|first2=Eckhard|last2=Völcker|first3=Guifré|last3=Torruella|title=On the Biology, Diversity and Evolution of Nucleariid Amoebae (Amorphea, Obazoa, Opisthokonta)|journal=Protist|volume=173|issue=4|date=17 June 2022|article-number=125895|doi=10.1016/j.protis.2022.125895|doi-access=free|pmid=35841659|hdl=2117/369912|hdl-access=free}}</ref> This clade is, in turn, closely related to Holozoa, the clade containing animals and their closest protist relatives. Together, they form the clade Opisthokonta. After animals and fungi, nucleariids include the third known occurrence of multicellularity among opisthokonts:{{efn|Excluding the colony formation found across holozoan protists, particularly choanoflagellates and ichthyosporeans, which can be considered multicellular to some degree.<ref name="Brown-2009"/>}} the species ''Fonticula alba'', a type of slime mold, capable of aggregative multicellular fruiting that develops sorocarps (stalks with masses of spores) for dispersal. The existence of ''Fonticula alba'' suggests that opisthokonts have a great propensity toward multicellularity.<ref name="Brown-2009"/>
{{clade|label1=Obazoa|1={{clade |1=Apusomonadida, Breviatea 70px |label2=Opisthokonta|2={{clade |1=Holozoa (animals and relatives) 50px |label2=Holomycota|2={{clade |1=Fungi 50px |2='''Nucleariids''' 50px }} }} }} }}
Nucleariids are unique within their greater evolutionary context. Apusomonads (relatives of opisthokonts), holozoans and fungi all evolved from ancestors that were single-celled phagotrophic flagellates. Opisthokonts, in particular, are characterized by a single posterior flagellum. Even the most basal-branching fungi (aphelids, rozellids and microsporidia){{efn|The aphelids, rozellids and microsporidia are sometimes interpreted as protists<ref name="Galindo-2022">{{Cite journal |last1=Galindo |first1=Luis Javier |last2=Torruella |first2=Guifré |last3=López-García |first3=Purificación |last4=Ciobanu |first4=Maria |last5=Gutiérrez-Preciado |first5=Ana |last6=Karpov |first6=Sergey A |last7=Moreira |first7=David |date=2023 |title=Phylogenomics Supports the Monophyly of Aphelids and Fungi and Identifies New Molecular Synapomorphies |journal=Systematic Biology|volume=72 |issue=3 |pages=505–515 |doi=10.1093/sysbio/syac054 |pmid=35900180 }}</ref> instead of fungi,<ref name="Tedersoo-2018"/><ref>{{Cite journal |display-authors=6 |vauthors=Wijayawardene NN, Hyde KD, Al-Ani LK, Tedersoo L, Haelewaters D, Rajeshkumar KC, Zhao RL, Aptroot A, Leontyev DV, Saxena RK, Tokarev YS, Dai DQ, Letcher PM, Stephenson SL, Ertz D, Lumbsch HT, Kukwa M, Issi IV, Madrid H, Phillips AJ, Selbmann L, Pfliegler WP, Horváth E, Bensch K, Kirk PM, Kolaříková K, Raja HA, Radek R, Papp V, Dima B, Ma J, Malosso E, Takamatsu S, Rambold G, Gannibal PB, Triebel D, Gautam AK, Avasthi S, Suetrong S, Timdal E, Fryar SC, Delgado G, Réblová M, Doilom M, Dolatabadi S, Pawłowska J, Humber RA, Kodsueb R, Sánchez-Castro I, Goto BT, Silva DK, de Souza FA, Oehl F, da Silva GA, Silva IR, Błaszkowski J, Jobim K, Maia LC, Barbosa FR, Fiuza PO, Divakar PK, Shenoy BD, Castañeda-Ruiz RF, Somrithipol S, Lateef AA, Karunarathna SC, Tibpromma S, Mortimer PE, Wanasinghe DN, Phookamsak R, Xu J, Wang Y, Tian F, Alvarado P, Li DW, Kušan I, Matočec N, Maharachchikumbura SS, Papizadeh M, Heredia G, Wartchow F, Bakhshi M, Boehm E, Youssef N, Hustad VP, Lawrey JD, Santiago AL, Bezerra JD, Souza-Motta CM, Firmino AL, Tian Q, Houbraken J, Hongsanan S, Tanaka K, Dissanayake AJ, Monteiro JS, Grossart HP, Suija A, Weerakoon G, Etayo J, Tsurykau A, Vázquez V, Mungai P, Damm U, Li QR, Zhang H, Boonmee S, Lu YZ, Becerra AG, Kendrick B, Brearley FQ, Motiejūnaitė J, Sharma B, Khare R, Gaikwad S, Wijesundara DS, Tang LZ, He MQ, Flakus A, Rodriguez-Flakus P, Zhurbenko MP, McKenzie EH, Stadler M, Bhat DJ, Liu JK, Raza M, Jeewon R, Nassonova ES, Prieto M, Jayalal RG, Erdoğdu M, Yurkov A, Schnittler M, Shchepin ON, Novozhilov YK, Silva-Filho AG, Liu P, Cavender JC, Kang Y, Mohammad S, Zhang LF, Xu RF, Li YM, Dayarathne MC, Ekanayaka AH, Wen TC, Deng CY, Pereira OL, Navathe S, Hawksworth DL, Fan XL, Dissanayake LS, Kuhnert E, Grossart HP, Thines M |title = Outline of Fungi and fungus-like taxa |journal=Mycosphere |year=2020 |volume=11 |issue=1 |pages=1060–1456 |url=http://www.mycosphere.org/pdf/MYCOSPHERE_11_1_8-1.pdf |issn=2077-7019 |doi=10.5943/mycosphere/11/1/8 |pmid= |doi-access=free }}</ref> depending on the authors.}} are single-celled flagellates that prey on other eukaryotes.<ref name="Galindo-2022"/> The last common ancestor of nucleariids, however, had lost the opisthokont flagellum and its cell polarity, and had gained the characteristic mucous coat.<ref name="Gabaldón-2022"/> The presence of filopodia is more common among opisthokonts, shared with aphelids<ref name="Galindo-2022"/> and most holozoans.<ref>{{cite journal|last1=Shalchian-Tabrizi|first1=Kamran|last2=Minge|first2=Marianne A.|last3=Espelund|first3=Mari|last4=Orr|first4=Russell|last5=Ruden|first5=Torgeir|last6=Jakobsen|first6=Kjetill S.|last7=Cavalier-Smith|first7=Thomas|author-link7=Thomas Cavalier-Smith|date=7 May 2008|title=Multigene Phylogeny of Choanozoa and the Origin of Animals|journal=PLOS ONE|volume=3|issue=5|article-number=e2098|doi=10.1371/journal.pone.0002098|doi-access=free |pmid=18461162 |pmc=2346548 |bibcode=2008PLoSO...3.2098S }}</ref>
== Classification ==
===History===
The history of the classification of nucleariids is full of incongruence between morphology and molecular phylogeny. Toward the end of the 19th century, most nucleariid species had already been described, and were classified with other naked or scaled filose amoebae.<ref name="Penard-1904">{{cite book|last1=Penard|first1=Eugène|author-link1=Eugène Penard|title=Les héliozoaires d'eau douce|trans-title=The freshwater heliozoans|language=French|publisher=W. Kündig & fils|date=1904|location=Genève|doi=10.5962/bhl.title.1407|oclc=8236527|id={{BHL page|1095193}}|doi-access=free|url=https://archive.org/details/leshliozoaires00pena}}</ref><ref name="Gabaldón-2022"/> During the second half of the 20th century, naturalist Heinrich Rainer described a subgroup of heliozoans, '''Rotosphaeridia''', to accommodate non-flagellated, scaled, filose amoebae without axopodia (the nucleariids ''Pompholyxophrys'', ''Pinaciophora'', ''Lithocolla'' and ''Rhabdiophrys'').<ref name="Rainer-1968">{{cite book|last1=Rainer|first1=Heinrich|title=Urtiere, Protozoa; Wurzelfüẞler, Rhizopoda; Sonnentierchen, Heliozoa: Systematik und Taxonomie, Biologie, Verbreitung und Ökologie der Arten der Erde|trans-title=Protozoa; Rhizopods; Heliozoa: systematics and taxonomy, biology, distribution and ecology of the species of the Earth|language=German|date=1968|series=Die Tierwelt Deutschlands und der angrenzenden Meeresteile [The animal world of Germany and the adjacent sea areas]|volume=56|publisher=VEB Gustav Fischer Verlag|location=Jena|oclc=5630582}}</ref>
Protozoologists John P. Cann and Frederick C. Page established the family '''Nucleariidae''' to include the naked genera ''Nuclearia'', ''Gobiella'' and ''Nucleosphaerium''<ref name="Cann-1979">{{cite journal|last1=Cann|first1=J. P.|last2=Page|first2=F. C.|title=''Nucleosphaerium tuckeri'' nov. gen. nov. sp. – a new freshwater filose amoeba without motile form in a new family Nucleariidae (Filosea: Aconchulinida) feeding by ingestion only|journal=Archiv für Protistenkunde|volume=122|date=1979|issue=3–4|pages=226–240|doi=10.1016/S0003-9365(79)80034-2}}</ref> (later synonymized with ''Nuclearia'').<ref name="Cann-1986">{{cite journal|last1=Cann|first1=John P.|date=August 1986|title=The feeding behavior and structure of ''Nuclearia delicatula''|journal=Journal of Protozoology|volume=33|issue=3|pages=392–396|doi=10.1111/j.1550-7408.1986.tb05629.x}}</ref> Through studies of their fine cellular ultrastructure via transmission electron microscopy, the order '''Cristidiscoidida''' was established within the class Filosea, to accommodate both families Nucleariidae and the silica-scaled '''Pompholyxophryidae''' (e.g., ''Pompholyxophrys'', ''Pinaciophora'' and ''Rhabdiophrys''), because they all shared disc-shaped mitochondrial cristae as a common characteristic (i.e., they were discicristate).<ref name="Page-1987">{{cite journal|last=Page|first=Frederick C.|title=The classification of 'naked' amoebae (Phylum Rhizopoda)|journal=Archiv für Protistenkunde|volume=133|issue=3–4|date=1987|pages=199–217|doi=10.1016/S0003-9365(87)80053-2}}</ref><ref name="Patterson-2000">{{cite book|chapter=Amoebae of uncertain affinities|first1=D. J.|last1=Patterson|first2=A. G. B.|last2=Simpson|first3=A.|last3=Rogerson|pages=804–827|chapter-url=https://protistologists.org/wp-content/uploads/2023/07/19AMOEBAE_OF_UNCERTAIN_AFFINITIES.pdf|title=The Illustrated Guide to the Protozoa: organisms traditionally referred to as protozoa, or newly discovered groups|editor-first1=John J.|editor-last1=Lee|editor-first2=Gordon F.|editor-last2=Leedale|editor-first3=Phyllis|editor-last3=Bradbury|volume=II|edition=2nd|publisher=Society of Protozoologists|url=https://protistologists.org/publications/illustrated-guide-to-the-protozoa/|author-link1=David J. Patterson|date=2000}}</ref><ref name="Gabaldón-2022"/>
The genus ''Fonticula'' was continually excluded, as it was considered an acrasid<ref name="Worley-1979">{{cite journal|first1=Ann C.|last1=Worley|first2=Kenneth B.|last2=Raper|first3=Marianne|last3=Hohl|title=''Fonticula alba'': a new cellular slime mold (Acrasiomycetes)|journal=Mycologia|volume=71|date=1979|issue=4|pages=746–760|doi=10.1080/00275514.1979.12021068}}</ref> or a slime mold,<ref name="Deasey-1981">{{cite journal|first1=Mary C.|last1=Deasey|first2=Lindsay S.|last2=Olive|title=Role of Golgi apparatus in sorogenesis by the cellular slime mold ''Fonticula alba''|journal=Science|volume=213|issue=4507|pages=561–563|doi=10.1126/science.213.4507.561|date=31 July 1981|pmid=17794844 |bibcode=1981Sci...213..561D }}</ref> until 1993, when protozoologist Thomas Cavalier-Smith created the subclass '''Cristidiscoidia''' to house two orders: '''Nucleariida''' (with Nucleariidae and Pompholyxophryidae) and '''Fonticulida''' (with Fonticulidae).<ref name="Cavalier-Smith-1993">{{cite journal|last1=Cavalier-Smith|first1=Thomas|author-link=Thomas Cavalier-Smith|title=Kingdom Protozoa and its 18 phyla|journal=Microbiological Reviews|date=1993|volume=57 |pages=953–994|pmc=372943|pmid=8302218|doi= 10.1128/mr.57.4.953-994.1993|issue=4 |bibcode=1993MbRev..57..953C }}</ref><ref name="Gabaldón-2022"/> However, he later considered scaled nucleariids (Pompholyxophryidae) as members of the Cercozoa, completely separate from naked ones,<ref>{{cite journal|last1=Cavalier-Smith|first1=Thomas|author-link=Thomas Cavalier-Smith|last2=Chao|first2=Ema E.|title=''Oxnerella micra'' sp. n. (Oxnerellidae fam. n.), a tiny naked centrohelid, and the diversity and evolution of Heliozoa|volume=163|issue=4|date=July 2012|pages=574–601|doi=10.1016/j.protis.2011.12.005|journal=Protist|pmid=22317961 }}</ref> but this is no longer accepted.<ref name="Galindo-2019"/> In a 1999 taxonomic revision by Kirill A. Mikrjukov, Cristidiscoidida was regarded as a junior synonym of Rotosphaerida, which finally united all discicristate filose amoebae. He also included ''Belonocystis''<ref name="Mikrjukov-1999">{{cite journal|first1=Kirill A.|last1=Mikrjukov|title=Taxonomic revision of scale-bearing heliozoon-like amoebae (Pompholyxophryidae, Rotosphaerida)|journal=Acta Protozoologica|volume=38|issue=2|pages=119–131|date=1999|url=https://rcin.org.pl/dlibra/publication/17718/edition/13534/content}}</ref> and ''Micronuclearia'' in this order,<ref name="Mikrjukov-2001">{{cite journal|last1=Mikrjukov|first1=Kirill A.|last2=Mylnikov|first2=Alexander P.|title=A study of the fine structure and the mitosis of a lamellicristate amoeba, ''Micronuclearia podoventralis'' gen. et sp. nov. (Nucleariidae, Rotosphaerida)|journal=European Journal of Protistology|volume=37|issue=1|date=2001|doi=10.1078/0932-4739-00783|pages=15–24}}</ref> which now are known to belong to Amoebozoa and CRuMs, respectively.<ref name="Gabaldón-2022"/>
At present, different conflicting classifications for nucleariids remain in use depending on the authors. Cavalier-Smith maintained his system through the years, using the name '''Cristidiscoidea''' as a class of his paraphyletic phylum Choanozoa, which included all protists most closely related to animals and fungi.<ref name="Ruggiero-2015">{{cite journal|first1=Michael A.|last1=Ruggiero|first2=Dennis P.|last2=Gordon|first3=Thomas M.|last3=Orrell|first4=Nicolas|last4=Bailly|first5=Thierry|last5=Bourgoin|first6=Richard C.|last6=Brusca|first7=Thomas|last7=Cavalier-Smith|author-link7=Thomas Cavalier-Smith|first8=Michael D.|last8=Guiry|author-link8=Michael D. Guiry|first9=Paul M.|last9=Kirk|title=A higher level classification of all living organisms|journal=PLOS ONE|date=29 April 2015|doi-access=free|doi=10.1371/journal.pone.0119248|volume=10|issue=4|article-number=e0119248|pmid=25923521|pmc=4418965|bibcode=2015PLoSO..1019248R }}</ref> Mycologists have proposed a separate kingdom '''Nucleariae''' with lower ranks for Cavalier-Smith's two orders (phyla '''Nuclearida''' and '''Fonticulida''', classes '''Nuclearidea''' and '''Fonticulidea'''), but without specifying their taxonomic composition.<ref name="Tedersoo-2018"/> Generally, protistologists prefer using the order Rotosphaerida instead, as it has priority over more recent names.<ref name="Mikrjukov-1999"/><ref name="Adl-2019">{{cite journal | doi=10.1111/JEU.12691 | title=Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes | date=26 September 2018| last1=Adl | first1=Sina M. | last2=Bass | first2=David | last3=Lane | first3=Christopher E. | last4=Lukeš | first4=Julius | last5=Schoch | first5=Conrad L. | last6=Smirnov | first6=Alexey | last7=Agatha | first7=Sabine | last8=Berney | first8=Cedric | last9=Brown | first9=Matthew W. | last10=Burki | first10=Fabien | last11=Cárdenas | first11=Paco | last12=Čepička | first12=Ivan | last13=Chistyakova | first13=Lyudmila | last14=Del Campo | first14=Javier | last15=Dunthorn | first15=Micah | last16=Edvardsen | first16=Bente | last17=Eglit | first17=Yana | last18=Guillou | first18=Laure | last19=Hampl | first19=Vladimír | last20=Heiss | first20=Aaron A. | last21=Hoppenrath | first21=Mona | last22=James | first22=Timothy Y. | last23=Karnkowska | first23=Anna | last24=Karpov | first24=Sergey | last25=Kim | first25=Eunsoo | last26=Kolisko | first26=Martin | last27=Kudryavtsev | first27=Alexander | last28=Lahr | first28=Daniel J.G. | last29=Lara | first29=Enrique | last30=Le Gall | first30=Line | journal=The Journal of Eukaryotic Microbiology | volume=66 | issue=1 | pages=4–119 | pmid=30257078 | pmc=6492006}} </ref><ref name="Galindo-2019"/> Most studies using the name Cristidiscoidea have only included ''Nuclearia'' or environmental sequences, while those using Rotosphaerida have been used when studying the scale-bearing amoebae and, more recently, the naked ones as well.<ref name="Gabaldón-2022"/>
At the family-level rank, although historically both Nucleariidae and Pompholyxophryidae have been used separately for naked and scale-bearing nucleariids respectively,<ref name="Mikrjukov-1999"/> and Fonticulidae solely for ''Fonticula'',<ref name="Cavalier-Smith-1993"/> protistologists tend to use only Nucleariidae now,<ref name="Patterson-2000"/><ref name="Gabaldón-2022"/> as there is no clear evolutionary separation between the three families.<ref name="Galindo-2019"/>
===Genera===
Of all nucleariids, only a few have been isolated and molecularly analyzed.<ref name="Galindo-2019">{{cite journal|first1=Luis Javier|last1=Galindo|first2=Guifré|last2=Torruella|first3=David|last3=Moreira|first4=Yana|last4=Eglit|first5=Alastair G. B.|last5=Simpson|first6=Eckhard|last6=Völcker|first7=Steffen|last7=Clauẞ|first8=Purificación|last8=López-García|title=Combined cultivation and single-cell approaches to the phylogenomics of nucleariid amoebae, close relatives of fungi|journal= Philosophical Transactions of the Royal Society B: Biological Sciences|date=7 October 2019|volume=374|issue=1786 |article-number=20190094|doi=10.1098/rstb.2019.0094|pmid=31587649 |pmc=6792443 }}</ref> Many genera remain as ''incertae sedis'' due to the lack of molecular data,<ref name="Adl-2012">{{cite journal|first1=Sina M.|last1=Adl|first2=Alastair G. B.|last2=Simpson|first3=Christopher E.|last3=Lane|first4=Julius|last4=Lukeš|first5=David|last5=Bass|first6=Samuel S.|last6=Bowser|first7=Matthew W.|last7=Brown|first8=Fabien|last8=Burki|first9=Micah|last9=Dunthorn|first10=Vladimir|last10=Hampl|first11=Aaron|last11=Heiss|first12=Mona|last12=Hoppenrath|first13=Enrique|last13=Lara|first14=Line|last14=le Gall|first15=Denis H.|last15=Lynn|first16=Hilary|last16=McManus|first17=Edward A. D.|last17=Mitchell|first18=Sharon E.|last18=Mozley-Stanridge|first19=Laura W.|last19=Parfrey|first20=Jan|last20=Pawlowski|first21=Sonja|last21=Rueckert|first22=Laura|last22=Shadwick|first23=Conrad L.|last23=Schoch|first24=Alexey|last24=Smirnov|first25=Frederick W.|last25=Spiegel|title=The Revised Classification of Eukaryotes|journal=The Journal of Eukaryotic Microbiology|date=28 September 2012|volume=59|issue=2|pages=429–514|doi=10.1111/j.1550-7408.2012.00644.x|doi-access=free|pmc=3483872|pmid=23020233}}</ref> as it is difficult to confirm their evolutionary position other than by morphological similarity. The following is a list of nucleariid genera with definite placement:<ref name="Patterson-2000"/><ref name="Gabaldón-2022"/> * ''Fonticula'' {{au|Worley, Raper & Hohl 1979}}<ref name="Worley-1979"/> * ''Lithocolla'' {{au|Schulze 1874}} * ''Nuclearia'' <small>Cienkowski 1865</small> (=''Nuclearella'' {{au|Frenzel 1897}}; ''Nuclearina'' {{au|Frenzel 1897}}; ''Nucleosphaerium'' {{au|Cann & Page 1979}}) * ''Parvularia'' <small>López-Escardó 2017</small><ref name="López-Escardó-2017">{{Cite journal|last1=López-Escardó|first1=David|last2=López-García|first2=Purificación|last3=Moreira|first3=David|last4=Ruiz-Trillo|first4=Iñaki|last5=Torruella|first5=Guifré|title=Parvularia atlantis gen. et sp. nov., a Nucleariid Filose Amoeba (Holomycota, Opisthokonta)|journal=Journal of Eukaryotic Microbiology|volume=65|issue=2|language=en|pages=170–179|doi=10.1111/jeu.12450|pmid=28741861|issn=1550-7408|year=2017|pmc=5708529}}</ref> * ''Pompholyxophrys'' {{au|Archer 1869}} (=''Hyalolampe'' {{au|Greeff 1869}}<ref name="Mikrjukov-1999"/>
The following are genera regarded as possibly belonging to this order:<ref name="Patterson-2000"/><ref name="Gabaldón-2022"/> * ''Elaeorhanis'' {{au|Greef, 1873}} (=''Lithosphaerella'' {{au|Frenzel 1897}}; ''Estrella'' {{au|Frenzel 1897}}) – may also be related to ''Diplophrys'', a member of the labyrinthulomycete order Amphitremida.<ref>{{cite journal|first1=Yuki|last1=Takahashi|first2=Masaki|last2=Yoshida|first3=Isao|last3=Inouye|first4=Makoto M.|last4=Watanabe|title=''Fibrophrys columna'' gen. nov., sp. nov: a member of the family Amphifilidae|volume=56|date=October 2016|pages=41–50|doi=10.1016/j.ejop.2016.06.003|journal=European Journal of Protistology|pmid=27468745 |url=https://tsukuba.repo.nii.ac.jp/records/40243 }}</ref> * ''Pinaciophora'' {{au|Greeff 1869}} (=''Pinacocystis'' {{au|Hertwig & Lesser 1874}}; ''Pinaciocystis'' {{au|Roskin 1929}}; ''Potamodiscus'' {{au|Gerloff 1968}})<ref name="Mikrjukov-1999"/> * ''Rabdiaster'' {{au|Mikrjukov 1999}}<ref name="Mikrjukov-1999"/> * ''Rabdiophrys'' {{au|Rainer 1968}}<ref name="Rainer-1968"/> * ''Thomseniophora'' {{au|Nicholls 2012}}<ref>{{cite journal|first1=Kenneth H.|last1=Nicholls|date=17 September 2012|title=New and little-known marine species of ''Pinaciophora'', ''Rabdiaster'' and ''Thomseniophora'' gen. nov. (Rotosphaerida: Pompholyxophryidae)|journal=Journal of the Marine Biological Association of the United Kingdom|volume=93|issue=5|pages=1211–1229|doi=10.1017/S002531541200135X}}</ref> * ''Vampyrellidium'' {{au|Zopf 1885}}
==Notes== {{Notelist|25em}}
==References== {{Reflist}}
{{Life on Earth}} {{Eukaryota}} {{Opisthokont protists}} {{Taxonbar|from1=Q15129670|from2=Q15129663|from3=Q55711231|from4=Q21447207|from5=Q1048747|from6=Q13403500}}
Category:Holomycota Category:Nucleariids