Excavata

For an explanation of very similar terms, see Eukaryota.
Excavata
Temporal range: Neoproterozoic–present
Giardia lamblia, a parasitic diplomonad
Scientific classification Edit this classification
(obsolete as paraphyletic)
Domain: Eukaryota
(unranked): Excavata
(Cavalier-Smith), 2002
Phyla and classes

see text

Three types of excavate cells. Top: Jakobida, 1-nucleus, 2-anterior flagellum, 3-ventral/posterior flagellum, 4-ventral feeding groove. Middle: Euglenozoa, 1-nucleus, 2-flagellar pocket/reservoir, 3-dorsal/anterior flagellum, 4-ventral/posterior flagellum, 5-cytostome/feeding apparatus. Bottom: Metamonada, 1-anterior flagella, 2-parabasal body, 3-undulating membrane, 4-posterior flagellum, 5-nucleus, 6-axostyle.

Excavata is an extensive and diverse but paraphyletic group of unicellular Eukaryota.[1][2] The group was first suggested by Simpson and Patterson in 1999[3][4] and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas.[5] Excavates were formerly considered to be included in the now obsolete Protista kingdom.[6] They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged (they have a distinctive ultrastructural identity).[4] They are considered to be a basal flagellate lineage.[7]

On the basis of phylogenomic analyses, the group was shown to contain three widely separated eukaryote groups, the discobids, metamonads, and malawimonads.[8][9][10][11] A current view of the composition of the excavates is given below, indicating that the group is paraphyletic. Except for some Euglenozoa, all are non-photosynthetic.

  1. ^ Hampl, Vladimir; Hug, Laura; Leigh, Jessica W.; et al. (2009). "Phylogenomic analyses support the monophyly of Excavata and resolve relationships among eukaryotic "supergroups"". PNAS. 106 (10): 3859–3864. Bibcode:2009PNAS..106.3859H. doi:10.1073/pnas.0807880106. PMC 2656170. PMID 19237557.
  2. ^ Simpson, Alastair G. B.; Inagaki, Yuji; Roger, Andrew J. (2006). "Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of "primitive" eukaryotes". Molecular Biology and Evolution. 23 (3): 615–625. doi:10.1093/molbev/msj068. PMID 16308337.
  3. ^ Simpson, Alastair G.B.; Patterson, David J. (December 1999). "The ultrastructure of Carpediemonas membranifera (Eukaryota) with reference to the 'excavate hypothesis'". European Journal of Protistology. 35 (4): 353–370. doi:10.1016/S0932-4739(99)80044-3.
  4. ^ a b Simpson, Alastair G. B. (November 2003). "Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)". International Journal of Systematic and Evolutionary Microbiology. 53 (6): 1759–1777. doi:10.1099/ijs.0.02578-0. PMID 14657103.
  5. ^ Dawkins, Richard; Wong, Yan (2016). The Ancestor's Tale. Houghton Mifflin Harcourt. ISBN 978-0544859937.
  6. ^ Cavalier-Smith, Thomas (2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". International Journal of Systematic and Evolutionary Microbiology. 52 (2): 297–354. doi:10.1099/00207713-52-2-297. PMID 11931142.
  7. ^ Dawson, Scott C.; Paredez, Alexander R. (2013). "Alternative cytoskeletal landscapes: cytoskeletal novelty and evolution in basal excavate protists". Current Opinion in Cell Biology. 25 (1): 134–141. doi:10.1016/j.ceb.2012.11.005. PMC 4927265. PMID 23312067.
  8. ^ Burki, Fabien; Roger, Andrew J.; Brown, Matthew W.; et al. (January 2020). "The New Tree of Eukaryotes". Trends in Ecology & Evolution. 35 (1): 43–55. doi:10.1016/j.tree.2019.08.008. PMID 31606140. S2CID 204545629.
  9. ^ Cite error: The named reference Brown_2018 was invoked but never defined (see the help page).
  10. ^ Heiss, Aaron A.; Kolisko, Martin; Ekelund, Fleming; et al. (4 April 2018). "Combined morphological and phylogenomic re-examination of malawimonads, a critical taxon for inferring the evolutionary history of eukaryotes". Royal Society Open Science. 5 (4): 171707. Bibcode:2018RSOS....571707H. doi:10.1098/rsos.171707. PMC 5936906. PMID 29765641.
  11. ^ Keeling, Patrick J.; Burki, Fabien (19 August 2019). "Progress towards the Tree of Eukaryotes". Current Biology. 29 (16): R808–R817. Bibcode:2019CBio...29.R808K. doi:10.1016/j.cub.2019.07.031. PMID 31430481.