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Metamonad

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The metamonads are a large group of flagellate amitochondriate Loukozoa. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well. These four groups are all anaerobic, occurring mostly as symbiotes of animals.

Metamonads
Giardia lamblia.jpg
Giardia lamblia, a parasitic diplomonad
Scientific classification
Domain:
(unranked):
Phylum:
Metamonada

Grassé 1952 emend. Cavalier-Smith 2003
Classes & orders

Contents

CharacteristicsEdit

A number of parabasalids and oxymonads are found in termite guts, 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.[1]

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 make up part of the excavates, a eukaryotic supergroup including flagellates with feeding grooves and their close relatives. Their relationships are uncertain,[2] 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 is based on works of Cavalier-Smith[3] with amendments within Fornicata from Yubukia, Simpson & Leander[4]

Metamonada were once again proposed to being basal eukaryotes in 2018.[5]

ReferencesEdit

  1. ^ 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.
  2. ^ 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.
  3. ^ Cavalier-Smith T (2013). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa". Europ. J. Protistol. 49 (2): 115–178. doi:10.1016/j.ejop.2012.06.001. PMID 23085100.
  4. ^ 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.
  5. ^ 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.

External linksEdit