A number of parabasalids and oxymonads are found in termiteguts, and play an important role in breaking down the cellulose found in wood. Some other metamonads are parasites.
These flagellates are unusual in lacking mitochondria. Originally they were considered among the most primitive eukaryotes, diverging from the others before mitochondria appeared. However, they are now known to have lost mitochondria secondarily, and retain both organelles and nuclear genes derived from them. Mitochondrial relics include hydrogenosomes, which produce hydrogen, and small structures called mitosomes.
It now appears the Metamonada are, together with Malawimonas, sister clades of the Podiata.[3]
All of these groups are united by having flagella or basal bodies in characteristic groups of four, which are often associated with the nucleus, forming a structure called a karyomastigont. In addition, the genera Carpediemonas and Trimastix are now known to be close relatives of the retortamonad-diplomonad line and the oxymonads, respectively. Both are free-living and amitochondriate.
Classificationedit
The metamonads were thought to make up part of the Excavata, a paraphyletic eukaryotic supergroup including flagellates with feeding grooves and their close relatives. Their relationships are uncertain,[4] and they do not always appear together on molecular trees. It is possible that the metamonads as defined here do not form a monophyletic subgroup.
The following higher level treatment from 2013 is based on works of Cavalier-Smith[5] with amendments within Fornicata from Yubukia, Simpson & Leander.[6]
Metamonada were once again proposed to be basal eukaryotes in 2018.[7]
Family Trichomonadidae Chalmers & Pekkoloa 1918 sensu Hampl et al. 2006
Order Honigbergiellida Čepička et al. 2010[11][10]
Family Honigbergiellidae Čepička, Hampl & Kulda 2010
Family Hexamastigidae Čepička, Hampl & Kulda 2010
Family Tricercomitidae Čepička, Hampl & Kulda 2010
Order Hypotrichomonadida Čepička et al. 2010
Family Hypotrichomonadidae (Honigberg 1963) Čepička, Hampl & Kulda 2010
Order Spirotrichonymphida Grassé 1952
Family Spirotrichonymphidae Grassé 1917
Order Tritrichomonadida Čepička et al. 2010
Family Dientamoebidae Grassé 1953
Family Monocercomonadidae Kirby 1944
Family Simplicimonadidae Čepička et al. 2010
Family Tritrichomonadidae Honigberg 1963
Order Cristamonadida Brugerolle & Patterson 2001 emend. Cavalier-Smith 2013
Family Calonymphidae Grassé 1911
Family Devescovinidae Doflein 1911
Referencesedit
^Stairs, Courtney W.; Táborský, Petr; Salomaki, Eric D.; Kolisko, Martin; Pánek, Tomáš; Eme, Laura; Hradilová, Miluše; Vlček, Čestmír; Jerlström-Hultqvist, Jon; Roger, Andrew J.; Čepička, Ivan (2021-12-20). "Anaeramoebae are a divergent lineage of eukaryotes that shed light on the transition from anaerobic mitochondria to hydrogenosomes". Current Biology. 31 (24): 5605–5612.e5. doi:10.1016/j.cub.2021.10.010. ISSN 0960-9822. PMID 34710348. S2CID 240054026.
^ abAl Jewari, Caesar; Baldauf, Sandra L. (2023-04-28). "An excavate root for the eukaryote tree of life". Science Advances. 9 (17): eade4973. Bibcode:2023SciA....9E4973A. doi:10.1126/sciadv.ade4973. ISSN 2375-2548. PMC10146883. PMID 37115919.
^Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (2016-06-01). "187-gene phylogeny of protozoan phylum Amoebozoa reveals a new class (Cutosea) of deep-branching, ultrastructurally unique, enveloped marine Lobosa and clarifies amoeba evolution". Molecular Phylogenetics and Evolution. 99: 275–296. doi:10.1016/j.ympev.2016.03.023. PMID 27001604.
^Cavalier-Smith T (November 2003). "The excavate protozoan phyla Metamonada Grassé emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa". Int. J. Syst. Evol. Microbiol. 53 (Pt 6): 1741–58. doi:10.1099/ijs.0.02548-0. PMID 14657102.
^Cavalier-Smith T (2013). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa". Eur. J. Protistol. 49 (2): 115–178. doi:10.1016/j.ejop.2012.06.001. PMID 23085100.
^Yubukia; Simpson; Leander (2013). "Comprehensive Ultrastructure of Kipferlia bialata Provides Evidence for Character Evolution within the Fornicata (Excavata)". Protist. 164 (3): 423–439. doi:10.1016/j.protis.2013.02.002. PMID 23517666.
^Krishnan, Arunkumar; Burroughs, A. Max; Iyer, Lakshminarayan; Aravind, L. (2018-07-04). "The unexpected provenance of components in eukaryotic nucleotide-excision-repair and kinetoplast DNA-dynamics from bacterial mobile elements". bioRxiv: 361121. doi:10.1101/361121.
^Zhang, Qianqian; Táborský, Petr; Silberman, Jeffrey D.; Pánek, Tomáš; Čepička, Ivan; Simpson, Alastair G.B. (2015). "Marine Isolates of Trimastix marina Form a Plesiomorphic Deep-branching Lineage within Preaxostyla, Separate from Other Known Trimastigids (Paratrimastix n. gen.)". Protist. 166 (4): 468–491. doi:10.1016/j.protis.2015.07.003. PMID 26312987.
^Radek, Renate; Platt, Katja; Öztas, Deniz; Šobotník, Jan; Sillam-Dussès, David; Hanus, Robert; Brune, Andreas (26 January 2023). "New insights into the coevolutionary history of termites and their gut flagellates: Description of Retractinympha glossotermitis gen. nov. sp. nov. (Retractinymphidae fam. nov.)". Frontiers in Ecology and Evolution. 11. doi:10.3389/fevo.2023.1111484.
^Cepicka, Ivan; Hampl, Vladimír; Kulda, Jaroslav (July 2010). "Critical Taxonomic Revision of Parabasalids with Description of one New Genus and three New Species". Protist. 161 (3): 400–433. doi:10.1016/j.protis.2009.11.005. PMID 20093080.