# Metamonad

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Clade of excavate protists

For an explanation of related terms, see [Excavata](/source/Excavata).

Metamonad Giardia lamblia, a parasitic diplomonad Scientific classification Domain: Eukaryota Clade: Metamonada Grassé 1952 emend. Cavalier-Smith 2003 Subgroups Fornicata Parabasalia Preaxostyla (=Anaeromonadea) Anaeramoebae (Anaeramoeba) Notopharyngea (=BaSk) Synonyms Archezoa Cavalier-Smith 1983 stat. n. emend. Cavalier-Smith 2022 Centrosomea Chatton Villeneuve 1937 Metamonadina Grassé 1952 Polymastigota Butschli 1884 Tetramastigota Hulsmann & Hausmann 1994

The **metamonads** are a large group of [flagellate](/source/Flagellate) [amitochondriate](/source/Amitochondriate) microscopic [eukaryotes](/source/Eukaryote). They include the [retortamonads](/source/Retortamonad), [diplomonads](/source/Diplomonad), [parabasalids](/source/Parabasalid), [oxymonads](/source/Oxymonad), and a range of more poorly studied taxa, most of which are free-living flagellates. All metamonads are [anaerobic](/source/Anaerobic_organism) (many being aerotolerant anaerobes), and most members of the four groups listed above are [symbiotes](/source/Symbiosis) or [parasites](/source/Parasitism) of animals, as is the case with [*Giardia lamblia*](/source/Giardia_duodenalis) which causes diarrhea in [mammals](/source/Mammal).[1]

## Characteristics

A number of parabasalids and oxymonads are found in [termite](/source/Termite) [guts](/source/Lower_gastrointestinal_tract), and play an important role in breaking down the [cellulose](/source/Cellulose) found in [wood](/source/Wood). Some other metamonads are [parasites](/source/Parasitism).

These flagellates are unusual in lacking aerobic [mitochondria](/source/Mitochondrion). Originally they were considered among the most primitive [eukaryotes](/source/Eukaryote), diverging from the others before mitochondria appeared. However, they are now known to have lost aerobic mitochondria secondarily, and retain both organelles and nuclear genes derived ultimately from the mitochondrial endosymbiont genome. Mitochondrial relics include [hydrogenosomes](/source/Hydrogenosome), which produce [hydrogen](/source/Hydrogen) (and make ATP), and small structures called [mitosomes](/source/Mitosome).

It now appears the Metamonada are, together with *[Malawimonas](/source/Malawimonas)*, sister [clades](/source/Clade) of the [Podiata](/source/Unikont).[2]

All of these groups have [flagella](/source/Flagellum) or basal bodies in characteristic groups of four (or more, in parabasalids), which are often associated with the [nucleus](/source/Cell_nucleus), forming a structure called a karyomastigont. In addition, genera such as *[Carpediemonas](/source/Carpediemonas)* and *[Trimastix](/source/Trimastix)* are now known to be close relatives of the retortamonad-diplomonad lineage and the oxymonads, respectively. Most of the closer relatives of the retortamonad-diplomonad lineage actually have two flagella and basal bodies.

## Classification

The metamonads were thought to make up part of the [Excavata](/source/Excavata), a proposed eukaryotic supergroup including flagellates with feeding grooves and their close relatives. Their relationships are uncertain,[3] and they do not always appear together on molecular trees. Current opinion is that Excavata is not a [monophyletic](/source/Monophyletic) group, but it might be [paraphyletic](/source/Paraphyly).

Metamonada were once again proposed to be basal eukaryotes in 2018.[4]

A view of the metamonad taxonomy is:[5][6][7][8][9][10][11][12][13][14][15][16][17][18]

- **Clade Metamonada** - Phylum [Fornicata](/source/Fornicata) - Order [Diplomonadida](/source/Diplomonad) - Family [Hexamitidae](/source/Diplomonad) - Subfamily [Hexamitinae](/source/Hexamitinae) - Subfamily [Giardiinae](/source/Giardiinae) - Order [Retortamonadida](/source/Retortamonad) (paraphyletic) - Family [Retortamonadidae](/source/Retortamonad) (paraphyletic) - Family [Caviomonadidae](https://en.wikipedia.org/w/index.php?title=Caviomonadidae&action=edit&redlink=1) - Informal group [*Carpediemonas*-like organisms](https://en.wikipedia.org/w/index.php?title=Carpediemonas-like_organisms&action=edit&redlink=1) ([polyphyletic](/source/Polyphyly)) - Order [Dysnectida](/source/Dysnectes) - Family [Dysnectidae](/source/Dysnectes) - Family [Kipferliidae](https://en.wikipedia.org/w/index.php?title=Kipferlia&action=edit&redlink=1) - Genus *[Aduncisulcus](https://en.wikipedia.org/w/index.php?title=Aduncisulcus&action=edit&redlink=1)* - Genus *[Carpediemonas](/source/Carpediemonas)* - Genus *[Ergobibamus](https://en.wikipedia.org/w/index.php?title=Ergobibamus&action=edit&redlink=1)* - Genus *[Hicanonectes](https://en.wikipedia.org/w/index.php?title=Hicanonectes&action=edit&redlink=1)* - Phylum [Parabasalia](/source/Parabasalid) - Class [Hypotrichomonadea](https://en.wikipedia.org/w/index.php?title=Hypotrichomonadida&action=edit&redlink=1) - Order [Hypotrichomonadida](https://en.wikipedia.org/w/index.php?title=Hypotrichomonadida&action=edit&redlink=1) - Family [Hypotrichomonadidae](https://en.wikipedia.org/w/index.php?title=Hypotrichomonadida&action=edit&redlink=1) - Class [Pimpavickea](https://en.wikipedia.org/w/index.php?title=Pimpavickea&action=edit&redlink=1) - Order [Pimpavickida](https://en.wikipedia.org/w/index.php?title=Pimpavickea&action=edit&redlink=1) - Family [Pimpavickidae](https://en.wikipedia.org/w/index.php?title=Pimpavickea&action=edit&redlink=1) - Class [Trichomonadea](https://en.wikipedia.org/w/index.php?title=Trichomonadea&action=edit&redlink=1) - Order [Honigbergiellida](https://en.wikipedia.org/w/index.php?title=Honigbergiellida&action=edit&redlink=1) - Family [Hexamastigidae](https://en.wikipedia.org/w/index.php?title=Hexamastix&action=edit&redlink=1) - Family [Honigbergiellidae](https://en.wikipedia.org/w/index.php?title=Honigbergiellidae&action=edit&redlink=1) - Family [Cthulhuidae](https://en.wikipedia.org/w/index.php?title=Cthulhuidae&action=edit&redlink=1) - Family [Tetratrichomastigidae](https://en.wikipedia.org/w/index.php?title=Tetratrichomastix&action=edit&redlink=1) - Order [Trichomonadida](/source/Trichomonadida) - Family [Lacusteriidae](https://en.wikipedia.org/w/index.php?title=Lacusteria&action=edit&redlink=1) - Family [Trichomonadidae](/source/Trichomonadidae) - Family *[Incertae sedis](/source/Incertae_sedis)* - Genus *[Pseudotrichomonas](https://en.wikipedia.org/w/index.php?title=Pseudotrichomonas&action=edit&redlink=1)* - Genus †*[Paleotrichomones](https://en.wikipedia.org/w/index.php?title=Paleotrichomones&action=edit&redlink=1)* - Clade [Tla](https://en.wikipedia.org/w/index.php?title=Tla_(clade)&action=edit&redlink=1) - Class [Lophomonadea](https://en.wikipedia.org/w/index.php?title=Lophomonadida&action=edit&redlink=1) - Order [Lophomonadida](https://en.wikipedia.org/w/index.php?title=Lophomonadida&action=edit&redlink=1) - Family [Lophomonadidae](https://en.wikipedia.org/w/index.php?title=Lophomonadida&action=edit&redlink=1) - Class [Trichonymphea](/source/Trichonymphida) - Order [Trichonymphida](/source/Trichonymphida) - Family [Barbulanymphidae](/source/Barbulanymphidae) - Family [Hoplonymphidae](https://en.wikipedia.org/w/index.php?title=Hoplonymphidae&action=edit&redlink=1) - Family [Retractinymphidae](https://en.wikipedia.org/w/index.php?title=Retractinympha&action=edit&redlink=1) - Family [Spirotrichosomidae](https://en.wikipedia.org/w/index.php?title=Spirotrichosomidae&action=edit&redlink=1) - Family [Staurojoeninidae](https://en.wikipedia.org/w/index.php?title=Staurojoeninidae&action=edit&redlink=1) - Family [Teranymphidae](https://en.wikipedia.org/w/index.php?title=Teranymphidae&action=edit&redlink=1) - Family [Trichonymphidae](/source/Trichonympha) - Family †[Burmanymphidae](https://en.wikipedia.org/w/index.php?title=Burmanymphus&action=edit&redlink=1) - Clade [Cadamassta](https://en.wikipedia.org/w/index.php?title=Cadamassta&action=edit&redlink=1) - Class [Cristamonadea](https://en.wikipedia.org/w/index.php?title=Cristamonadea&action=edit&redlink=1) - Order [Calonymphida](https://en.wikipedia.org/w/index.php?title=Calonymphida&action=edit&redlink=1) - Family [Calonymphidae](https://en.wikipedia.org/w/index.php?title=Calonymphidae&action=edit&redlink=1) - Family [Deltotrichonymphidae](https://en.wikipedia.org/w/index.php?title=Deltotrichonymphidae&action=edit&redlink=1) - Family [Mixotrichidae](/source/Mixotricha) - Order [Devescovinida](https://en.wikipedia.org/w/index.php?title=Devescovinidae&action=edit&redlink=1) - Family [Devescovinidae](https://en.wikipedia.org/w/index.php?title=Devescovinidae&action=edit&redlink=1) - Order [Gigantomonadida](/source/Gigantomonas) - Family [Gigantomonadidae](/source/Gigantomonas) - Order *Incertae sedis* - Genus *[Cyclojoenia](https://en.wikipedia.org/w/index.php?title=Cyclojoenia&action=edit&redlink=1)* - Genus *[Joenia](https://en.wikipedia.org/w/index.php?title=Joenia&action=edit&redlink=1)* - Genus *[Joenina](https://en.wikipedia.org/w/index.php?title=Joenina&action=edit&redlink=1)* - Genus *[Joenoides](https://en.wikipedia.org/w/index.php?title=Joenoides&action=edit&redlink=1)* - Genus *[Joenopsis](https://en.wikipedia.org/w/index.php?title=Joenopsis&action=edit&redlink=1)* - Genus *[Pachyjoenia](https://en.wikipedia.org/w/index.php?title=Pachyjoenia&action=edit&redlink=1)* - Genus *[Parajoenopsis](https://en.wikipedia.org/w/index.php?title=Parajoenopsis&action=edit&redlink=1)* - Genus *[Placojoenia](https://en.wikipedia.org/w/index.php?title=Placojoenia&action=edit&redlink=1)* - Genus *[Projoenia](https://en.wikipedia.org/w/index.php?title=Projoenia&action=edit&redlink=1)* - Class [Dientamoebea](https://en.wikipedia.org/w/index.php?title=Dientamoebea&action=edit&redlink=1) - Order [Dientamoebida](https://en.wikipedia.org/w/index.php?title=Dientamoebea&action=edit&redlink=1) - Family [Dientamoebidae](https://en.wikipedia.org/w/index.php?title=Dientamoebea&action=edit&redlink=1) - Class [Monocercomonadea](/source/Monocercomonas) - Order [Monocercomonadida](/source/Monocercomonas) - Family [Monocercomonadidae](/source/Monocercomonas) - Class [Simplicimonadea](https://en.wikipedia.org/w/index.php?title=Simplicimonas&action=edit&redlink=1) - Order [Simplicimonadida](https://en.wikipedia.org/w/index.php?title=Simplicimonas&action=edit&redlink=1) - Family [Simplicimonadidae](https://en.wikipedia.org/w/index.php?title=Simplicimonas&action=edit&redlink=1) - Class [Tritrichomonadea](/source/Tritrichomonas) - Order [Tritrichomonadida](/source/Tritrichomonas) - Family [Tritrichomonadidae](/source/Tritrichomonas) - Class [Spirotrichonymphea](https://en.wikipedia.org/w/index.php?title=Spirotrichonymphea&action=edit&redlink=1) - Order [Cononymphida](https://en.wikipedia.org/w/index.php?title=Cononympha&action=edit&redlink=1) - Family [Cononymphidae](https://en.wikipedia.org/w/index.php?title=Cononympha&action=edit&redlink=1) - Order [Holomastigotoidida](https://en.wikipedia.org/w/index.php?title=Holomastigotoididae&action=edit&redlink=1) - Family [Holomastigotoididae](https://en.wikipedia.org/w/index.php?title=Holomastigotoididae&action=edit&redlink=1) - Order [Spirotrichonymphida](https://en.wikipedia.org/w/index.php?title=Spirotrichonymphida&action=edit&redlink=1) - Family [Brugerollinidae](https://en.wikipedia.org/w/index.php?title=Brugerollinidae&action=edit&redlink=1) - Family [Fraterculidae](https://en.wikipedia.org/w/index.php?title=Fraterculidae&action=edit&redlink=1) - Family [Holomastigotidae](https://en.wikipedia.org/w/index.php?title=Holomastigotidae&action=edit&redlink=1) - Family [Spirotrichonymphidae](https://en.wikipedia.org/w/index.php?title=Spirotrichonymphidae&action=edit&redlink=1) - Class *Incertae sedis* - Genus *[Chilomitus](https://en.wikipedia.org/w/index.php?title=Chilomitus&action=edit&redlink=1)* - Genus *[Rhizonympha](https://en.wikipedia.org/w/index.php?title=Rhizonympha&action=edit&redlink=1)* - Genus *[Tricercomitus](https://en.wikipedia.org/w/index.php?title=Tricercomitus&action=edit&redlink=1)* - Genus *[Trichocovina](https://en.wikipedia.org/w/index.php?title=Trichocovina&action=edit&redlink=1)* - Phylum [Preaxostyla](/source/Preaxostyla) - Order [Oxymonadida](/source/Oxymonad) - Family [Oxymonadidae](https://en.wikipedia.org/w/index.php?title=Oxymonadidae&action=edit&redlink=1) - Family [Pyrsonymphidae](https://en.wikipedia.org/w/index.php?title=Pyrsonymphidae&action=edit&redlink=1) - Family [Streblomastigidae](/source/Streblomastix) - Family [Saccinobaculidae](/source/Saccinobaculus) - Family [Polymastigidae](https://en.wikipedia.org/w/index.php?title=Polymastigidae&action=edit&redlink=1) - Order [Trimastigida](/source/Trimastix) - Family [Trimastigidae](/source/Trimastix) - Order [Paratrimastigida](/source/Paratrimastix) - Family [Paratrimastigidae](/source/Paratrimastix) - Phylum [Anaeramoebae](/source/Anaeramoeba) - Family [Anaeramoebidae](/source/Anaeramoeba) - Class [Notopharyngea](#BaSk_clade) - Order [Barthelonida](/source/Barthelonid) - Family [Barthelonidae](/source/Barthelonid) - Order [Skoliomonadida](/source/Skoliomonas) - Family [Skoliomonadidae](/source/Skoliomonas)

## Evolution

Within Metamonada, two main branches are recovered in recent [phylogenetic analyses](/source/Phylogenetic_analyses). One branch contains the [Parabasalia](/source/Parabasalia) and the closely related [anaeramoebae](/source/Anaeramoebae). The other branch contains two large groups: the [Fornicata](/source/Fornicata), which is closely related to [barthelonids](/source/Barthelonid)[13] and the recently isolated *[Skoliomonas](/source/Skoliomonas)*;[14] and the [Preaxostyla](/source/Preaxostyla).[12]

A 2023 study found it likely that Metamonada is a [paraphyletic](/source/Paraphyly) group at the base of Eukaryota, meaning their anaerobic metabolism possibly represents the ancestral condition in eukaryotes (similar to what the [Archezoa](/source/Archezoa)-[Metakaryota](/source/Metakaryota) hypothesis proposed) and that aerobic mitochondria might not have the same origin as hydrogenosomes.[1]

## References

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## External links

- [Tree of Life: Fornicata](http://tolweb.org/Fornicata/121182)

v t e Eukaryote classification Domain Archaea Bacteria Eukaryota (major groups Metamonada Discoba Diaphoretickes Hacrobia Cryptista Rhizaria Alveolata Stramenopiles Plants Amorphea Amoebozoa Opisthokonta Animalia Fungi Mesomycetozoea) Amorphea Amoebozoa Discosea Tubulinea Variosea Archamoebea Cutosea Eumycetozoa (true slime molds) Obazoa Apusomonadida Breviatea Opisthokonta Holomycota Nucleariidae Fungi¹ Holozoa Tunicaraptor †Bicellum Ichthyosporea Pluriformea Filozoa Filasterea Choanozoa Choanoflagellata Animalia (animals)¹ Diaphoretickes Telonemia Haptista Centroplasthelida Haptophytina SAR Rhizaria Cercozoa Endomyxa Retaria Foraminifera Radiolaria* Alveolata Colponemida* Ciliophora (ciliates) Myzozoa Apicomplexa Chrompodellida Dinoflagellata Perkinsozoa Stramenopiles Platysulcus Kaonashia Commation Bigyra* Bicosoecida Placidozoa Sagenista Gyrista Developea Pirsoniales Hyphochytriomycetes Ochrophyta (brown algae, diatoms and relatives) Oomycota (water molds) Actinophryida CAM Pancryptista Microheliella Cryptista Palpitomonas Katablepharidida Cryptomonada Archaeplastida (plants sensu lato) Picozoa Rhodophyta (red algae) Rhodelphidia Glaucophyta Viridiplantae (green plants or plants sensu stricto) Prasinodermophyta Chlorophyta Streptophyta Mesostigmatophyceae Chlorokybophyceae Spirotaenia Klebsormidiophyceae Charophyceae Coleochaetophyceae Zygnematophyceae Embryophyta (land plants or plants sensu strictissimo)¹ Disparia Provora Nebulidia Nibbleridia Membrifera Caelestes Hemimastigophora "Excavates"* Discoba Jakobea Tsukubamonas Discicristata Heterolobosea Euglenozoa Metamonada* Anaeramoebidae Parabasalia Barthelona Skoliomonas Fornicata Preaxostyla Malawimonadida Malawimonadidae Imasidae Incertae sedis Ancyromonadida Ancyromonadidae Planomonadidae Divimonas CRuMs Diphylleida Mantamonadida Rigifilida Glissandrida Genera of uncertain affiliation Acinetactis Berkeleyaesol Kamera Magosphaera Meringosphaera Meteora Parakaryon (?) Phyllomitus Quasibodo Tetrahelia Acritarchs and other fossils †Acritarcha †Algospongia †Archaeochaeta †Calcitarcha †Calpionellida †Cephalonyx †Changchengia †Cheleutochroa †Chitinozoa †Coryphidium †Cucumiforma †Dictyosphaera †Diskagma (?) †Eosolena †Francevillian biota (?) †Germinosphaera †Grandilingulata †Granomarginata †Grypania †Gunflint microbiota †Horodyskia †Introvertocystis †Korilophyton †Leiosphaeridia †Navifusa †Portalites †Protosterol biota †Prototaxites †Pterospermopsimorpha †Qingshania †Quadrisporites †Schizofusa †Shuiyousphaeridium †Simia †Tappania †Tawuia (?) †Tetraporina †Thuchomyces (?) †Tuanshanzia †Valeria †Vernanimalcula ¹non-protist groups *possibly paraphyletic groups bold denotes groups with over 1,000 species Taxonomy of protists

v t e "Excavata" Domain Archaea Bacteria Eukaryota (major groups Metamonada Discoba Diaphoretickes Hacrobia Cryptista Rhizaria Alveolata Stramenopiles Plants Amorphea Amoebozoa Opisthokonta Animalia Fungi Mesomycetozoea) Discoba Jakobida Jakobea Jakobida Agogoniidae Andaluciidae Histionidae Jakobidae Moramonadidae Ophirinidae Stygiellidae Tsukubamonada Tsukubea Tsukubamonadida Tsukubamonadidae Discicristata Percolozoa Pharyngomonada Pharyngomonadidea Pharyngomonadida Pharyngomonadidae Tetramitia Lunosea Selenaionida Selenaionidae Neovahlkampfiea Neovahlkampfiida Neovahlkampfiidae Eutetramitia Lyromonadea Lyromonadida Gruberellidae Paravahlkampfiidae Plaesiobystridae Psalteriomonadidae Heterolobosea Acrasida Acrasidae Naegleriida Tulamoebidae Naegleriidae Tetramitida Vahlkampfiidae Creneida Creneidae Percolomonadida Barbeliidae Lulidae Percolomonadidae Stephanopogonidae Euglenozoa Postgaardia Postgaardea Bihospitida Bihospitidae Postgaardida Calkinsiidae Postgaardidae Glycomonada Diplonemea Diplonemida Diplonemidae Eupelagonemidae Hemistasiidae Kinetoplastea Bordnamonadidae Trypanophididae Prokinetoplastina Prokinetoplastida Ichthyobodonidae Perkinselidae Metakinetoplastina Neobodonida Allobodonidae Neobodonidae Rhynchomonadidae Parabodonida Parabodonidae Trypanoplasmatidae Bodonida Bodonidae Trypanosomatida Trypanosomatidae Euglenida Petalomonadea Petalomonadida Petalomonadidae Sphenomonadidae Alistosa Decastavida Decastavidae Keelungiidae Lentomonadidae Heterostavida Sphenomonadidae Ploeotiida Sphenomonadidae Entosiphonea Entosiphonida Entosiphonidae Karavia Hemiolia Liburna Spirocuta Anisonemea Anisonemida Anisonemidae Heteronematales Heteronemataceae Natomonadida Astasiidae Distigmidae Neometanemidae Peranemea Acroglissida Teloproctidae Peranematida Peranemataceae Euglenophyceae Rapazida Rapazidae Euglenomonadales Euglenomonadaceae Eutreptiales Eutreptiaceae Euglenales Euglenaceae Euglenamorphaceae Euglenocapsaceae Phacaceae Loukozoa Neolouka Malawimonadea Malawimonadida Imasidae Malawimonadidae Ancyromonadida Ancyromonadidae Planomonadidae Metamonada Anaeromonada Anaeromonadea Paratrimastigida Paratrimastigidae Trimastigida Trimastigidae Oxymonadida Oxymonadidae Polymastigidae Pyrsonymphidae Saccinobaculidae Streblomastigidae Trichozoa Fornicata Kipferliidae Carpediemonadea Carpediemonadida Carpediemonadidae Eopharyngia Diplomonadida Giardiidae Octomitidae Spironucleidae Hexamitidae Dysnectida Dysnectidae Retortamonadida Caviomonadidae Chilomastigidae Retortamonadidae Parabasalia Pimpavickea Pimpavicka Pimpavickidae Hypotrichomonadea Hypotrichomonadida Hypotrichomonadidae Trichomonadea Honigbergiellida Cthulhuidae Hexamastigidae Honigbergiellidae Tetratrichomastigidae Tricercomitidae Lophomonadida Lophomonadidae Trichomonadida Lacusteriidae Trichomonadidae Trichonymphida Barbulanymphidae †Burmanymphidae Hoplonymphidae Spirotrichosomidae Retractinymphidae Staurojoeninidae Teratonymphidae Trichonymphidae Spirotrichonymphea Cononymphida Cononymphidae Cristamonadida Calonymphidae Deltotrichonymphidae Devescovinidae Gigantomonadidae Mixotrichidae Holomastigotoidida Holomastigotoididae Monocercomonadida Monocercomonadidae Simplicimonadida Simplicimonadidae Spirotrichonymphida Brugerollinidae Fraterculidae Holomastigotidae Spirotrichonymphidae Tritrichomonadida Dientamoebidae Tritrichomonadidae

Taxon identifiers Metamonada Wikidata: Q499091 Wikispecies: Metamonada AlgaeBase: 99783 CoL: 53 EoL: 6825402 GBIF: 7813133 IRMNG: 245 NZOR: b4b7d43b-6fe7-49cd-9d9e-ac1b8474979e WoRMS: 562592

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Adapted from the Wikipedia article [Metamonad](https://en.wikipedia.org/wiki/Metamonad) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Metamonad?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.