{{short description|Class of protists that produce a filamentous network}} {{Automatic taxobox | image = Aplanonet3.jpg | image_caption = Cell with network of ectoplasmic filaments (''Aplanochytrium'' sp.) | image_alt = | taxon = Labyrinthulomycetes | authority = Arx, 1970, Dick, 2001 | subdivision_ranks = Orders | subdivision_ref = <ref name="ADL_2019"/> | subdivision = *Amphitremida *Amphifilida *Oblongichytrida *Labyrinthulida *Thraustochytrida | synonyms = * Labyrinthulomycota <small>Whittaker, 1969</small> * Labyrinthomorpha <small>Page in Levine et al., 1980</small> * Labyrinthulea <small>Olive, 1975<br/> ''ex'' Cavalier-Smith, 1989</small> }}
'''Labyrinthulomycetes''' (ICNafp) or '''Labyrinthulea'''<ref name="CAVALIER-SMITH_1997"/> (ICZN) is a class of protists that produce a network of filaments or tubes,<ref name="TSUI_2009"/> which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrinthulids (or slime nets) and thraustochytrids. They are mostly marine, commonly found as parasites on algae and seagrasses or as decomposers on dead plant material. They also include some parasites of marine invertebrates and mixotrophic species that live in a symbiotic relationship with zoochlorella.<ref name="SCHÄRER_2007"/><ref name="PAN_2016"/><ref name="GOMAA_2013"/>
== Characteristics == {{unreferenced section|date=August 2023}} Although they are outside the cells, the filaments of Labyrinthulomycetes are surrounded by a membrane. They are formed and connected with the cytoplasm by a unique organelle called a sagenogen or bothrosome. The cells are uninucleated and typically ovoid, and move back and forth along the amorphous network at speeds varying from 5-150 μm per minute. Among the labyrinthulids, the cells are enclosed within the tubes, and among the thraustochytrids, they are attached to their sides.<ref>{{Citation |last=Latimer |first=Jessica |title=Phylogeny and morphology of novel Labyrinthulomycetes in Nova Scotia, Canada |date=2026-01-15 |url=http://biorxiv.org/lookup/doi/10.64898/2026.01.15.699578 |access-date=2026-05-16 |language=en |doi=10.64898/2026.01.15.699578 |last2=Ozsan |first2=Eda |last3=Goertz |first3=Tj |last4=Kaur |first4=Gurnoor |last5=Chung |first5=Dudley |last6=Archibald |first6=John M.}}</ref>
== Evolution == === Evolutionary origin === Labyrinthulomycetes are not fungi, but a monophyletic group of eukaryotes within the Stramenopiles. They belong to the phylum Bigyra, which contains other heterotrophic microorganisms such as the bicosoecids. Considering that the plastids from Stramenopiles are possibly the result of an event of endosymbiosis in their last common ancestor, the bicosoecids and the labyrinthulomycetes could have originated from a mixotrophic algal common ancestor that secondarily lost their plastids.<ref name="TSUI_2009"/>
Some characteristics of the labyrinthulomycetes can be explained by their origin from ancestral plastids. They produce omega-3 poly-unsaturated fatty acids using a desaturase usually present in chloroplasts. The zoospores of labyrinthulids have an eyespot composed of membrane-bound granules that resembles eyespots of photosynthetic stramenopiles, which are either within a plastid or believed to be derived from a plastid.<ref name="TSUI_2009"/>
Within Bigyra, the labyrinthulomycetes are the sister group to Eogyrea, a class containing the species ''Pseudophyllomitus vesiculosus'' and the environmental clade called MAST-4. Together they compose the subphylum Sagenista.<ref name="8phyla"/><ref name="THAKUR_2019"/>
{{clade|style=font-size:90%;|label1=Stramenopiles|1={{clade|2=Platysulcea|1={{clade|sublabel2=''plastid loss''|label2=Bigyra|2={{clade|label1=Opalozoa|1={{clade|1=Placidozoa 50px|2=Bicosoecida 50px}}|label2=Sagenista|2={{clade|1='''Labyrinthulomycetes''' 50px|2=Eogyrea}}}}|label1=Gyrista|1={{clade|1=Ochrophyta 50px|sublabel2=''plastid loss''|2=Pseudofungi 50px}}}}}}}}
== Classification == Labyrinthulomycetes or Labyrinthulea used to compose the defunct fungal phylum Labyrinthulomycota.<ref name="HANDBOOK_PROTISTS_14"/> They were originally considered unusual slime moulds, although they are not very similar to the other sorts. The structure of their zoospores and genetic studies show them to be a primitive group of heterokonts, but their classification and treatment remains somewhat unsettled.
This class usually contained two orders, Labyrinthulales and Thraustochytriales (ICBN), or Labyrinthulida and Thraustochytrida (ICZN), but a different classification has recently been proposed.<ref name="GOMAA_2013"/><ref name="ANDERSON_2012"/><ref name="FIORITO_2016"/><ref name="ADL_2019"/><ref name="HANDBOOK_PROTISTS_14"/>
* Order Labyrinthulales/Labyrinthulida {{au|E. A. Bessey 1950/Doffein 1901}} ** Family Aplanochytriaceae/Aplanochytriidae {{au|Leander ex Cavalier-Smith 2012}} *** ''Aplanochytrium'' {{au|Bahnweg & Sparrow 1972}} [=''Labyrinthuloides'' {{au|Perkins 1973}}] ** Family Labyrinthulaceae/Labyrinthulidae {{au|Haeckel 1868/Cinekowksa 1867}} *** ''Labyrinthomyxa'' {{au|Duboscq 1921}} *** ''Pseudoplasmodium'' {{au|Molisch 1925}} *** ''Labyrinthula'' {{au|Cienkowski 1864}} [=''Labyrinthodictyon'' {{au|Valkanov 1969}}; ''Labyrinthorhiza'' {{au|Chadefaud 1956}}] ** Family-level clade "Stellarchytriaceae/Stellarchytriidae" – this group is provisionally placed in Labyrinthulida<ref name="HANDBOOK_PROTISTS_14"/><ref name="ADL_2019"/> but, according to phylogenetic analyses, diverges before the rest of labyrinthulean clades.<ref name="FIORITO_2016"/> *** ''Stellarchytrium'' {{au|FioRito & Leander 2016}} * Order Oblongichytriales/Oblongichytrida ** Family Oblongichytriaceae/Oblongichytriidae {{au|Cavalier-Smith 2012}} *** ''Oblongichytrium'' {{au|Yokoyama & Honda 2007}} * Order Thraustochytriales/Thraustochytrida {{au|Sparrow 1973}} ** ''Pyrrhosorus'' <small>Juel 1901</small> ** ''Thanatostrea'' <small>Franc & Arvy 1969</small> ** Family Althornidiaceae/Althorniidae {{au|Jones & Alderman 1972}} *** ''Althornia'' {{au|Jones & Alderman 1972}} ** Family Thraustochytriacae/Thraustochytriidae {{au|Sparrow ex Cejp 1959}} *** ''Japanochytrium'' <small>Kobayasi & Ôkubo 1953</small> *** ''Monorhizochytrium'' <small>Doi & Honda 2017</small> *** ''Sicyoidochytrium'' <small>Yokoy., Salleh & Honda 2007</small> *** ''Aurantiochytrium'' <small>Yokoy. & Honda 2007</small> *** ''Ulkenia'' <small>Gaertn. 1977</small> *** ''Parietichytrium'' <small>Yokoy., Salleh & Honda 2007</small> *** ''Botryochytrium'' <small>Yokoy., Salleh & Honda 2007</small> *** ''Schizochytrium'' <small>Goldst. & Belsky emend. Booth & Mill.</small> *** ''Thraustochytrium'' <small>Sparrow 1936</small> *** ''Hondaea'' <small>Amato & Cagnac 2018</small> *** ''Labyrinthulochytrium'' <small>Hassett & Gradinger 2018</small><ref name="HASSETT_2018"/> * Order Amphitrematales/Amphitremida {{au|Gomaa et al. 2013}} ** Family "Amphitremidiaceae"/Amphitremidae {{au|Poch 1913}} *** ''Paramphitrema'' {{au|Valkanov 1970}} *** ''Archerella'' {{au|Loeblich & Tappan 1961}} *** ''Amphitrema'' {{au|Archer 1867}} ** Family "Diplophrydaceae"/Diplophryidae {{au|Cavalier-Smith 2012}} *** ''Diplophrys'' {{au|Barker 1868}} * Order "Amphifilales"/Amphifilida {{au|Cavalier Smith 2012}} ** Family Sorodiplophryidae <small>Cavalier-Smith 2012</small> *** ''Sorodiplophrys'' <small>Olive & Dykstra 1975</small> *** ''Fibrophrys'' <small>Takahashi et al. 2016</small> ** Family Amphifilidae <small>Cavalier-Smith 2012</small> *** Genus ''Amphifila'' <small>Cavalier-Smith 2012</small>
== Genetic code == The labyrinthulomycete ''Thraustochytrium aureum'' is notable for the alternative genetic code of its mitochondria which use {{mono|TTA}} as a stop codon instead of coding for Leucine.<ref name="WIDEMAN_2019"/> This code is represented by NCBI translation table 23, ''Thraustochytrium'' mitochondrial code.<ref name="NCBI_GENCODES"/>
{|class="wikitable" style="border: none; text-align: center;" |+ |- ! style="width: 250px;" | Genetic code !! style="width: 25px;" | Translation <br/> table !! style="width: 50px;" | DNA codon !! style="width: 50px;" | RNA codon !! colspan="3" style="width: 150px;" | Translation <br/> with this code !! style="border: none; width: 1px;" | !! style="width: 150px;" | Standard code<br />(Translation table 1) |- | rowspan="1" | ''Thraustochytrium'' mitochondrial || rowspan="1" | 23 || {{mono|TTA}} || {{mono|UUA}} || colspan="3" style="background-color:#B0B0B0;" | {{mono|STOP {{=}} Ter}} {{mono|(*)}} || style="border: none; width: 1px;" | || style="background-color:#ffe75f;" | {{mono|Leu}} {{mono|(L)}} |}
== Gallery == <gallery> File:Aplanolm.jpg|''Aplanochytrium'' sp. under light microscope File:Aplanosem.png|''Aplanochytrium'' sp. under SEM File:Aurantiochytrium limacinum SR21.jpg|''Aurantiochytrium'' sp. File:Collection Penard MHNG Specimen 48-2-4 Amphitrema stenostoma.tif|Test of ''Amphitrema'', a testate amoeba recently included in the group File:Tsenkovsky Lev Semyonovich.jpg|Leon Cienkowski, Russian botanist who in 1867 described ''Labyrinthula'', the first genus of the group<ref>Cienkowski, L. (1867). Ueber den Bau und die Entwicklung der Labyrinthuleen. ''Arch. mikr. Anat.'', 3:274, [https://www.biodiversitylibrary.org/item/110292#page/288/mode/1up].</ref> </gallery>
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<ref name="TSUI_2009">{{cite journal |first1=Clement K M|last1=Tsui|first2=Wyth|last2=Marshall|first3=Rinka|last3=Yokoyama|first4=Daiske|last4=Honda|first5=J Casey|last5=Lippmeier|first6=Kelly D|last6=Craven|first7=Paul D|last7=Peterson|first8=Mary L|last8=Berbee|title=Labyrinthulomycetes phylogeny and its implications for the evolutionary loss of chloroplasts and gain of ectoplasmic gliding |journal=Molecular Phylogenetics and Evolution|volume=50 |issue=1 |pages=129–40 |date=January 2009 |pmid=18977305 |doi=10.1016/j.ympev.2008.09.027 }}</ref>
<ref name="SCHÄRER_2007">{{Cite journal | doi = 10.1007/s00227-007-0755-4| title = Thraustochytrids as novel parasitic protists of marine free-living flatworms: ''Thraustochytrium caudivorum'' sp. nov. Parasitizes Macrostomum lignano| journal = Marine Biology| volume = 152| issue = 5| page = 1095| year = 2007| last1 = Schärer | first1 = L. | last2 = Knoflach | first2 = D. | last3 = Vizoso | first3 = D. B. | last4 = Rieger | first4 = G. | last5 = Peintner | first5 = U. | s2cid = 4836350| url = http://doc.rero.ch/record/319983/files/227_2007_Article_755.pdf}}</ref>
<ref name="PAN_2016">{{cite thesis |type=MSc |last=Pan |first=Jingwen|date=2016 |title=Labyrinthulomycetes diversity meta-analysis|publisher=University of British Columbia|url=https://open.library.ubc.ca/media/stream/pdf/24/1.0223199/3|doi=10.14288/1.0223199}}</ref>
<ref name="GOMAA_2013">{{cite journal|last1=Gomaa|first1=Fatma|last2=Mitchell|first2=Edward A. D.|last3=Lara|first3=Enrique|title=Amphitremida (poche, 1913) is a new major, ubiquitous labyrinthulomycete clade|journal=PLoS One|date=2013|volume=8|issue=1|article-number=e53046|doi=10.1371/journal.pone.0053046|pmid=23341921|pmc=3544814| bibcode= 2013PLoSO...853046G | doi-access= free }}</ref>
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}}
== External links == {{EB1911 Poster|Labyrinthulidea}} * [https://web.archive.org/web/20070417091256/http://www.botany.uga.edu/zoosporicfungi/labyrint.htm Labyrinthulomycota] {{wikispecies}} {{Heterokont}} {{Taxonbar|from1=Q1148791|from2=Q16653009|from3=Q131275915}} Category:Stramenopile classes Category:Bigyra