Amoebozoa: Wikis

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Amoebozoa
Fossil range: Neoproterozoic–Recent
Scientific classification
Domain: Eukaryota
(unranked) Unikonta
Kingdom: Amoebozoa
Lühe, 1913 emend.
Subgroups

Mycetozoa   (slime molds)
Archamoebae
Tubulinea
Flabellinea
Uncertain placement
   Acanthopodida
   Stereomyxida
   etc.

The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means of internal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like, called lobopodia. Most are unicellular, and are common in soils and aquatic habitats, with some found as symbiotes of other organisms, including several pathogens. The Amoebozoa also include the slime moulds, multinucleate or multicellular forms that produce spores and are usually visible to the unaided eye.

Amoebozoa vary greatly in size. Many are only 10-20 μm in size, but they also include many of the larger protozoa. The famous species Amoeba proteus may reach 800 μm in length, and partly on account of its size is often studied as a representative cell. Multinucleate amoebae like Chaos and Pelomyxa may be several millimetres in length, and some slime moulds cover several square feet.

Contents

Morphology

The cell is typically divided into a granular central mass, called endoplasm, and a clear outer layer, called ectoplasm. During locomotion the endoplasm flows forwards and the ectoplasm runs backwards along the outside of the cell. Many amoeba move with a definite anterior and posterior; in essence the cell functions as a single pseudopod. They usually produce numerous clear projections called subpseudopodia (or determinate pseudopodia), which have a defined length and are not directly involved in locomotion.

Other amoebozoans may form multiple indeterminate pseudopodia, which are more or less tubular and are mostly filled with granular endoplasm. The cell mass flows into a leading pseudopod, and the others ultimately retract unless it changes direction. Subpseudopodia are usually absent. In addition to a few naked forms like Amoeba and Chaos, this includes most amoebae that produce shells. These may be composed of organic materials, as in Arcella, or of collected particles cemented together, as in Difflugia, with a single opening through which the pseudopodia emerge.

The primary mode of nutrition is by phagocytosis: the cell surrounds potential food particles, sealing them into vacuoles where the may be digested and absorbed. Some amoebae have a posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell. When food is scarce, most species can form cysts, which may be carried aerially and introduce them to new environments. In slime moulds, these structures are called spores, and form on stalked structures called fruiting bodies or sporangia.

Most Amoebozoa lack flagella and more generally do not form microtubule-supported structures except during mitosis. However, flagella occur among some archamoebae, and many slime moulds produce biflagellate gametes. The flagellum is generally anchored by a cone of microtubules, suggesting a close relationship to the opisthokonts. The mitochondria characteristically have branching tubular cristae, but have been lost among archamoebae.

Classification

Amoebae are difficult to classify, and relationships within the phylum remain confused.

It appears (based in proteomes) that the amoebozoa form a sister group to animals and fungi, diverging from this lineage after it had split from the plants,[1] as illustrated below:


Plants




Amoebozoa




Animals



Fungi





Strong similarities between Amoebozoa and Opisthokonts (including animals and fungi) lead to the proposal that they form a clade called Unikonts.

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Lobose amoebozoa

Traditionally all amoebae with lobose pseudopods were treated together as the Lobosea, placed with other amoeboids in the phylum Sarcodina or Rhizopoda, but these were considered to be unnatural groups. Structural and genetic studies identified the percolozoans and several archamoebae as independent groups. In phylogenies based on rRNA their representatives were separate from other amoebae, and appeared to diverge near the base of eukaryotic evolution, as did most slime molds.

However, revised trees by Cavalier-Smith and Chao in 1996[2] suggested that the remaining lobosans do form a monophyletic group, and that the archamoebae and Mycetozoa are closely related to it, although the percolozoans are not. Subsequently they emended the older phylum Amoebozoa to refer to this supergroup.[3] Studies based on other genes have provided strong support for the unity of this group.[4] Patterson treated most with the testate filose amoebae as the ramicristates[5], based on mitochondrial similarities, but the latter are now removed to the Cercozoa.

The subphylum Lobosa is paraphyletic. Two major classes of Lobosa have been identified, the Tubulinea and Flabellinea, but various others remain of uncertain placement.

Other amoebozoa

The archamoebae and Mycetozoa have been placed in a subphylum Conosa. This classification receives some support from molecular phylogenies.

Fossil record

Vase-shaped microfossils (VSMs) discovered around the world show that amoebozoans have existed since the Neoproterozoic Era. The fossil species Melanocyrillium hexodiadema, Palaeoarcella athanata, and Hemisphaeriella ornata come from rocks 750 million years old. All three VSMs share a hemispherical shape, invaginated aperture, and regular indentations, that strongly resemble modern arcellinids, which are shell-bearing amoeboids. P. athanata in particular looks the same as the extant genus Arcella.[6] [7]

List of amoeboid protozoa pathogenic to humans

References

  1. ^ Eichinger, L.; Pachebat, J.A.; Glöckner, G.; Rajandream, M.A.; Sucgang, R.; Berriman, M.; Song, J.; Olsen, R.; Szafranski, K.; Xu, Q.; Others, (2005). "The genome of the social amoeba Dictyostelium discoideum". Nature 435 (7038): 43–57. doi:10.1038/nature03481.  
  2. ^ Cavalier-Smith, T. & Chao, E.E. (1996). "Molecular phylogeny of the free-living archezoan Trepomonas agilis and the nature of the first eukaryote". Journal of Molecular Evolution 43: 551–562. doi:10.1007/BF02202103.  
  3. ^ Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews of the Cambridge Philosophical Society 73: 203–266. doi:10.1017/S0006323198005167.  
  4. ^ Baldauf, S.L. et al. (2000). "A kingdom-level phylogeny of eukaryotes based on combined protein data". Science 290: 972–977. doi:10.1126/science.290.5493.972. PMID 11062127.  
  5. ^ David J. Patterson (1999). "The Diversity of Eukaryotes". American Naturalist 145: S96–S124.  
  6. ^ Porter, Susannah H., Meisterfeld, Ralf, and Knoll, Andrew H. (2003). "Vase-shaped microfossils from the Neoproterozoic Chuar Group, Grand Canyon: a classification guided by modern testate amoebae". Journal of Paleontology 77 (3): 409–429. doi:10.1666/0022-3360(2003)077<0409:VMFTNC>2.0.CO;2.  
  7. ^ Porter, Susannah M. (2006), "The Proterozoic Fossil Record of Heterotrophic Eukaryotes", in Xiao, Shuhai; Kaufman, Alan J., Neoproterozoic Geolobiology and Paleobiology, 27, Dordrecht, The Netherlands: Springer, pp. 1–21, doi:10.1007/1-4020-5202-2, http://www.springerlink.com/content/p4w2552254x1q317/  

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

Translingual

Etymology

From Latin.

Proper noun

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Wikipedia

Amoebozoa

  1. a taxonomic phylum, within kingdom Protista - the amoebae and slime moulds

Related terms

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Wikispecies


Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Phylum: Amoebozoa
Subphyla: Conosa - Lobosa - Protamoebae
[list of subphyla after Cavalier-Smith (2009: 26, 'Amoebozoa are here grouped in three subphyla ...')]

References

primary references

  • Cavalier-Smith, T. 2009: Megaphylogeny, cell body plans, adaptive zones: causes and timing of eukaryote basal radiations. Journal of eukaryotic microbiology, 56: 26-33. DOI: 10.1111/j.1550-7408.2008.00373.x Abstract
  • Minge, M.A.; Silberman, J.D.; Orr, R.J.S.; Cavalier-Smith, T.; Shalchian-Tabrizi, K.; Burki, F.; Skjæveland, A.; Jakobsen, K.S. 2009: Evolutionary position of breviate amoebae and the primary eukaryote divergence. Proceedings of the Royal Society (B), 276: 597-604. DOI: 10.1098/rspb.2008.1358

additional references

  • Adl, S.M. et al. 2005: The new higher level classification of eukaryotes with emphasis on the taxonomy of protists. Journal of eukaryotic microbiology, 52(5): 399-451. PDF
  • Cavalier-Smith, T.; Chao, E.E.-Y.; Oates, B. 2004: Molecular phylogeny of Amoebozoa and the evolutionary significance of the unikont Phalansterium. European journal of protistology, 40: 21-48.
  • Nikolaev, S.I.; Berney, C.; Petrov, N.B.; Mylnikov, A.P.; Fahrni, J.F.; Pawlowski, J. 2006: Phylogenetic position of Multicilia marina and the evolution of Amoebozoa. International journal of systematic and evolutionary microbiology, 56: 1449-1458. DOI 10.1099/ijs.0.63763-0 PDF
  • Pawlowski, J.; Burki, F. 2009: Untangling the phylogeny of amoeboid protists. Journal of eukaryotic microbiology, 56: 16–25. DOI: 10.1111/j.1550-7408.2008.00379.x Abstract PDF

links

Vernacular names

English: amoebozoans
Français: Amibe
Lietuvių: Ameboidiniai
Português: Amebozoários
Türkçe: Kökbacaklılar
Wikimedia Commons For more multimedia, look at Amoebozoa on Wikimedia Commons.

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