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While most amoebozoans are "naked," like the familiar ''Amoeba'' and ''Chaos'', or covered with a loose coat of minute scales, like [[Cochliopodium]] and [[Korotnevella]], members of the order [[Arcellinida]] form rigid shells, or [[test (biology)|tests]], equipped with a single aperture through which the pseudopods emerge. Arcellinid tests may be secreted from of organic materials, as in ''[[Arcella]]'', or aggregated from collected particles cemented together, as in ''[[Difflugia|Difflugia.]] ''
While most amoebozoans are "naked," like the familiar ''Amoeba'' and ''Chaos'', or covered with a loose coat of minute scales, like [[Cochliopodium]] and [[Korotnevella]], members of the order [[Arcellinida]] form rigid shells, or [[test (biology)|tests]], equipped with a single aperture through which the pseudopods emerge. Arcellinid tests may be secreted from of organic materials, as in ''[[Arcella]]'', or aggregated from collected particles cemented together, as in ''[[Difflugia|Difflugia.]] ''


In all amoebozoa, the primary mode of nutrition is by [[phagocytosis]], in which the cell surrounds potential food particles with its pseudopods, sealing them into [[vacuole]]s within which they may be digested and absorbed. Some amoebozoans have a posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell.{{Citation needed|date = April 2015}} When food is scarce, most species can form [[cyst]]s, 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 [[sporangium|sporangia]].
In all amoebozoa, the primary mode of nutrition is [[phagocytosis]], in which the cell surrounds potential food particles with its pseudopods, sealing them into [[vacuole]]s within which they may be digested and absorbed. Some amoebozoans have a posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell.{{Citation needed|date = April 2015}} When food is scarce, most species can form [[cyst]]s, which may be carried aerially and introduce them to new environments.{{Citation needed|date = April 2015}} In slime moulds, these structures are called spores, and form on stalked structures called fruiting bodies or [[sporangium|sporangia]].


The majority of Amoebozoa lack [[flagellum|flagella]] and more generally do not form [[microtubule]]-supported structures except during [[mitosis]]. However, flagella occur among the A[[archamoebae|rchamoebae]], and many slime moulds produce biflagellate [[gamete]]s {{Citation needed|date=October 2011}}. The flagellum is generally anchored by a cone of microtubules, suggesting a close relationship to the [[opisthokont]]s. {{Citation needed|date = April 2015}} The [[mitochondrion|mitochondria]] in amoebozoan cells characteristically have branching tubular [[crista|cristae.]] However, among the [[Archamoebae]], which are adapted to anoxic or microaerophilic habitats, mitochondria have been lost.
The majority of Amoebozoa lack [[flagellum|flagella]] and more generally do not form [[microtubule]]-supported structures except during [[mitosis]]. However, flagella occur among the A[[archamoebae|rchamoebae]], and many slime moulds produce biflagellate [[gamete]]s {{Citation needed|date=October 2011}}. The flagellum is generally anchored by a cone of microtubules, suggesting a close relationship to the [[opisthokont]]s. {{Citation needed|date = April 2015}} The [[mitochondrion|mitochondria]] in amoebozoan cells characteristically have branching tubular [[crista|cristae.]] However, among the [[Archamoebae]], which are adapted to anoxic or microaerophilic habitats, mitochondria have been lost.
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}}
}}


Strong similarities between Amoebozoa and [[Opisthokont]]s have lead to the proposal that they form a distinct clade. Thomas Cavalier-Smith proposed the name "unikonts" (formally, Unikonta) for this branch, whose members were believed to have been descended from a common ancestor possessing a single emergent flagellum rooted in one [[basal body]].<sup>[1][2]</sup> However, recent work has shown that the hypothesis of a uniciliate ancestor is probably false. In their Revised Classification of Eukaryotes, Adl et al. proposed Amorphea as a more suitable name for a clade of approximately the same composition.<ref name=":1">{{Cite journal|url = http://www.ncbi.nlm.nih.gov/pubmed/23020233|title = The Revised Classification of Eukaryotes|last = Adl et al.|first = |date = September, 2012|journal = Journal of Eukaryotic Microbiology May-June 60(3):433|doi = 10.1111/j.1550-7408.2012.00644.x|pmid = 23020233|access-date = April 7, 2015}}</ref> More recent work places the members of Amorphea together with the [[malawimonas|malawimonids]] and [[collodictyon|collodictyonids]] in a proposed clade called Opimoda, which comprises one of two major lineages emerging from the root of the eukaryote tree of life.<ref name=":3">{{Cite journal|url = http://www.pnas.org/content/112/7/E693.abstract|title = Bacterial proteins pinpoint a single eukaryotic root|last = Derelle et al.|first = |date = 2015|journal = Proceedings of the National Academy of Sciences|doi = doi: 10.1073/pnas.1420657112|pmid = |access-date = April 7, 2015}}</ref>
Strong similarities between Amoebozoa and [[Opisthokont]]s have lead to the proposal that they form a distinct clade. Thomas Cavalier-Smith proposed the name "unikonts" (formally, Unikonta) for this branch, whose members were believed to have been descended from a common ancestor possessing a single emergent flagellum rooted in one [[basal body]].<sup>[1][2]</sup> However, while the close relationship between Amoebozoa and Opisthokonta is well supported, recent work has shown that the hypothesis of a uniciliate ancestor is probably false. In their Revised Classification of Eukaryotes, Adl et al. proposed Amorphea as a more suitable name for a clade of approximately the same composition.<ref name=":1">{{Cite journal|url = http://www.ncbi.nlm.nih.gov/pubmed/23020233|title = The Revised Classification of Eukaryotes|last = Adl et al.|first = |date = September, 2012|journal = Journal of Eukaryotic Microbiology May-June 60(3):433|doi = 10.1111/j.1550-7408.2012.00644.x|pmid = 23020233|access-date = April 7, 2015}}</ref> More recent work places the members of Amorphea together with the [[malawimonas|malawimonids]] and [[collodictyon|collodictyonids]] in a proposed clade called Opimoda, which comprises one of two major lineages diverging at the root of the eukaryote tree of life.<ref name=":3">{{Cite journal|url = http://www.pnas.org/content/112/7/E693.abstract|title = Bacterial proteins pinpoint a single eukaryotic root|last = Derelle et al.|first = |date = 2015|journal = Proceedings of the National Academy of Sciences|doi = doi: 10.1073/pnas.1420657112|pmid = |access-date = April 7, 2015}}</ref>


{{See also|Eukaryote#Phylogeny}}
{{See also|Eukaryote#Phylogeny}}
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| year = 1996 | volume = 43 | pages = 551–562 | doi=10.1007/BF02202103 | pmid=8995052 | issue=6
| year = 1996 | volume = 43 | pages = 551–562 | doi=10.1007/BF02202103 | pmid=8995052 | issue=6
}}
}}
</ref> 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.<ref>
</ref> suggested that the remaining lobosans do form a monophyletic group, to which the Archamoebae and Mycetozoa were closely related, although the percolozoans were not. Subsequently they emended the phylum Amoebozoa to include both the subphylum Lobosa and a new subphylum [[Conosa]] comprised of the Archamoebae and the [[Mycetozoa]].<ref>
{{cite journal | author=Cavalier-Smith, T.
{{cite journal | author=Cavalier-Smith, T.
| title = A revised six-kingdom system of life
| title = A revised six-kingdom system of life
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| year = 1998 | volume = 73 | pages = 203–266
| year = 1998 | volume = 73 | pages = 203–266
| doi = 10.1111/j.1469-185X.1998.tb00030.x | pmid=9809012 | issue=3}}
| doi = 10.1111/j.1469-185X.1998.tb00030.x | pmid=9809012 | issue=3}}
</ref>
</ref> Studies based on other genes have provided strong support for the unity of this group.<ref>{{cite doi|10.1126/science.290.5493.972}}</ref>
[[David J. Patterson|Patterson]] treated most testate amoebae with filose pseudopods as the ramicristates,<ref>
{{cite journal | first = David J. |last=Patterson
| title = The Diversity of Eukaryotes
| journal = American Naturalist
| url=http://starcentral.mbl.edu/eutree_workshop/protistiary/electronmicroscopy/Patterson_1999_amnat.PDF
| format=PDF
| pmid = 10527921 | year = 1999 | volume = 154 | pages = S96–S124 | doi=10.1086/303287 | issue = S4}}
</ref> based on mitochondrial similarities, but the latter are now removed to the [[Cercozoa]].


Phylogenetic work now appears to support a primary bifurcation within the Amoebozoa, dividing the group into two major subphyla: [[Lobosa]] and [[Conosa]]. The former consists largely of the classic Lobosea: non-flagellated amoebae with blunt, lobopose pseudopods. The latter is made up of both amoeboid and flagellated cells, characteristically with more pointed or slightly branching subpseudopodia.<ref name=":2">{{Cite journal|url = http://www.sciencedirect.com/science/article/pii/S1055790314002784|title = Multigene phylogeny resolves deep branching of Amoebozoa|last = Cavalier-Smith et al.|first = |date = 2015|journal = Molecular Phylogenetics and Evolution|doi = 10.1016/j.ympev.2014.08.011|pmid = |access-date = April 7, 2015}}</ref>
Molecular genetic data appear to support this primary division of the Amoebozoa into Lobosa and Conosa. The former consists largely of the classic Lobosea: non-flagellated amoebae with blunt, lobopose pseudopods (''Amoeba'', ''Acanthamoeba, Arcella, Difflugia etc.''). The latter is made up of both amoeboid and flagellated cells, characteristically with more pointed or slightly branching subpseudopodia (Archamoebae and the Mycetozoan slime molds).<ref name=":2">{{Cite journal|url = http://www.sciencedirect.com/science/article/pii/S1055790314002784|title = Multigene phylogeny resolves deep branching of Amoebozoa|last = Cavalier-Smith et al.|first = |date = 2015|journal = Molecular Phylogenetics and Evolution|doi = 10.1016/j.ympev.2014.08.011|pmid = |access-date = April 7, 2015}}</ref>


==Fossil record==
==Fossil record==

Revision as of 16:19, 7 April 2015

Amoebozoa
Temporal range: Neoproterozoic–Recent
Chaos carolinensis
Scientific classification
Domain:
Eukaryota
(unranked):
Unikonta
Phylum:
Amoebozoa

Lühe, 1913 emend. Cavalier-Smith, 1998
Subphyla and Infraphyla
Synonyms
  • Eumycetozoa Zopf 1884, emend Olive 1975

Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, most of which possess blunt, lobose pseudopods and tubular mitochondrial cristae.[1][2][3] In most classification schemes, Amoebozoa is ranked as a phylum within either the kingdom Protista[4] or the kingdom Protozoa.[5] In the classification scheme favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota.[2]

Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Most phylogenetic trees identify it as the sister group to Opisthokonta, the major clade which contains both Fungi and Animals as well as some 300 species of unicellular protists.[3][1] Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta,[6] Amorphea[2] or Opimoda.[7]

The group includes many of the best-known amoeboid organisms, such as Chaos, Entamoeba, Pelomyxa and the genus Amoeba itself. Species of Amoebozoa may be either testate (shelled), coated with scales, or naked, and cells may possess flagella. Free-living species are common in both salt and freshwater, as well as soil, moss and leaf litter. Some live as parasites or symbiotes of other organisms, and some are known to cause disease in humans and other organisms.

While the majority of amoebozoan species are unicellular, the group also includes several varieties of slime molds, which have a macroscopic, multicellular stage of life during which individual amoeboid cells aggregate to produce spores.

Amoebozoa vary greatly in size. Some are only 10–20 μm in diameter, while others are among the largest protozoa. The well-known species Amoeba proteus, which may reach 800 μm in length, is often studied in schools and laboratories as a representative cell or model organism, partly because of its convenient size. Multinucleate amoebae like Chaos and Pelomyxa (the so-called "giant amoebae") may be several millimetres in length, and some multicellular amoebozoa, like the "dog vomit" slime mold Fuligo septica, can cover an area of several square meters.[8]

Morphology

Amoebozoa is a large and diverse group, but certain features are common to many of its members. The amoebozoan 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. In motion, many amoebozoans have a clearly defined anterior and posterior and may assume a "monopodial" form, with the entire cell functioning as a single pseudopod. Large pseudopods may produce numerous clear projections called subpseudopodia (or determinate pseudopodia), which are extended to a certain length and then retracted, either for the purposed of locomotion or food intake. A cell may also form multiple indeterminate pseudopodia, through which the entire contents of the cell flow in the direction of locomotion. These 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 the organism changes direction.[9]

While most amoebozoans are "naked," like the familiar Amoeba and Chaos, or covered with a loose coat of minute scales, like Cochliopodium and Korotnevella, members of the order Arcellinida form rigid shells, or tests, equipped with a single aperture through which the pseudopods emerge. Arcellinid tests may be secreted from of organic materials, as in Arcella, or aggregated from collected particles cemented together, as in Difflugia.

In all amoebozoa, the primary mode of nutrition is phagocytosis, in which the cell surrounds potential food particles with its pseudopods, sealing them into vacuoles within which they may be digested and absorbed. Some amoebozoans have a posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell.[citation needed] When food is scarce, most species can form cysts, which may be carried aerially and introduce them to new environments.[citation needed] In slime moulds, these structures are called spores, and form on stalked structures called fruiting bodies or sporangia.

The majority of Amoebozoa lack flagella and more generally do not form microtubule-supported structures except during mitosis. However, flagella occur among the Archamoebae, and many slime moulds produce biflagellate gametes [citation needed]. The flagellum is generally anchored by a cone of microtubules, suggesting a close relationship to the opisthokonts. [citation needed] The mitochondria in amoebozoan cells characteristically have branching tubular cristae. However, among the Archamoebae, which are adapted to anoxic or microaerophilic habitats, mitochondria have been lost.

Classification

Further information: wikispecies:Amoebozoa

It appears (based on molecular genetics) that the amoebozoa form a sister group to animals and fungi, diverging from this lineage after it had split from the other groups,[10] as illustrated below:

other groups

unikonts

Amoebozoa

Opisthokonta

Fungi

Animals

Strong similarities between Amoebozoa and Opisthokonts have lead to the proposal that they form a distinct clade. Thomas Cavalier-Smith proposed the name "unikonts" (formally, Unikonta) for this branch, whose members were believed to have been descended from a common ancestor possessing a single emergent flagellum rooted in one basal body.[1][2] However, while the close relationship between Amoebozoa and Opisthokonta is well supported, recent work has shown that the hypothesis of a uniciliate ancestor is probably false. In their Revised Classification of Eukaryotes, Adl et al. proposed Amorphea as a more suitable name for a clade of approximately the same composition.[2] More recent work places the members of Amorphea together with the malawimonids and collodictyonids in a proposed clade called Opimoda, which comprises one of two major lineages diverging at the root of the eukaryote tree of life.[7]

See also: Eukaryote § Phylogeny

Lobosa and Conosa

Traditionally all amoebozoa with lobose pseudopods were grouped together in the class 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[11] suggested that the remaining lobosans do form a monophyletic group, to which the Archamoebae and Mycetozoa were closely related, although the percolozoans were not. Subsequently they emended the phylum Amoebozoa to include both the subphylum Lobosa and a new subphylum Conosa comprised of the Archamoebae and the Mycetozoa.[12]

Molecular genetic data appear to support this primary division of the Amoebozoa into Lobosa and Conosa. The former consists largely of the classic Lobosea: non-flagellated amoebae with blunt, lobopose pseudopods (Amoeba, Acanthamoeba, Arcella, Difflugia etc.). The latter is made up of both amoeboid and flagellated cells, characteristically with more pointed or slightly branching subpseudopodia (Archamoebae and the Mycetozoan slime molds).[3]

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.[13][14]

List of amoeboid protozoa pathogenic to humans

References

  1. ^ a b Pawlowski; et al. (November 6, 2012). "CBOL Protist Working Group: Barcoding Eukaryotic Richness beyond the Animal, Plant, and Fungal Kingdoms". PLOS biology 10(11). doi:10.1371/journal.pbio.1001419. {{cite journal}}: Explicit use of et al. in: |last= (help)CS1 maint: unflagged free DOI (link)
  2. ^ a b c d Adl; et al. (September, 2012). "The Revised Classification of Eukaryotes". Journal of Eukaryotic Microbiology May-June 60(3):433. doi:10.1111/j.1550-7408.2012.00644.x. PMID 23020233. Retrieved April 7, 2015. {{cite journal}}: Check date values in: |date= (help); Explicit use of et al. in: |last= (help)
  3. ^ a b c Cavalier-Smith; et al. (2015). "Multigene phylogeny resolves deep branching of Amoebozoa". Molecular Phylogenetics and Evolution. doi:10.1016/j.ympev.2014.08.011. Retrieved April 7, 2015. {{cite journal}}: Explicit use of et al. in: |last= (help)
  4. ^ Corliss, John O. (1984). "The Kingdom Protista and its 45 Phyla". BioSystems 17.2 (1984): 87-126. doi:10.1016/0303-2647(84)90003-0. Retrieved April 7, 2015.
  5. ^ Cavalier-Smith, Thomas (2003). "Protist phylogeny and the high-level classification of Protozoa". European Journal of Protistology. doi:10.1078/0932-4739-00002.
  6. ^ Cavalier-Smith, Thomas (2003). "Protist phylogeny and the high-level classification of Protozoa". European Journal of Protistology. 39 (4): 338–348. doi:10.1078/0932-4739-00002.
  7. ^ a b Derelle; et al. (2015). "Bacterial proteins pinpoint a single eukaryotic root". Proceedings of the National Academy of Sciences. doi:doi: 10.1073/pnas.1420657112. Retrieved April 7, 2015. {{cite journal}}: Check |doi= value (help); Explicit use of et al. in: |last= (help)
  8. ^ "Zinc accumulation by the slime mold Fuligo septica (L.) Wiggers in the former Soviet Union and North Korea". Journal of Environment Quality. 31 (3): 1038–42. 2002. doi:10.2134/jeq2002.1038. PMID 12026071.
  9. ^ Jeon, Kwang W. (1973). Biology of Amoeba. New York: Academic Press. p. 100.
  10. ^ Eichinger, L.; Pachebat, J.A.; Glöckner, G.; Rajandream, M.A.; Sucgang, R.; Berriman, M.; Song, J.; Olsen, R.; Szafranski, K.; Xu, Q. (2005). "The genome of the social amoeba Dictyostelium discoideum". Nature. 435 (7038): 43–57. doi:10.1038/nature03481. PMC 1352341. PMID 15875012.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ 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 (6): 551–562. doi:10.1007/BF02202103. PMID 8995052.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews of the Cambridge Philosophical Society. 73 (3): 203–266. doi:10.1111/j.1469-185X.1998.tb00030.x. PMID 9809012.
  13. ^ Porter, Susannah H.; Meisterfeld, Ralf; 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Porter, Susannah M. (2006). "The Proterozoic Fossil Record of Heterotrophic Eukaryotes". In Xiao, Shuhai; Kaufman, Alan J. (eds.). Neoproterozoic Geolobiology and Paleobiology. Vol. 27. Dordrecht, The Netherlands: Springer. pp. 1–21. doi:10.1007/1-4020-5202-2.
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