Amoebozoa
518489
224593508
2008-07-09T15:53:34Z
Vojtech.dostal
6298480
[[cs:Amoebozoa]]
{{Taxobox
| fossil_range = [[Neoproterozoic]]{{Dubious|date=March 2008}} - [[Recent]]
| image = Chaos diffluens.jpg
| image_width = 240px
| image_caption = ''[[Chaos (amoeba)|Chaos diffluens]]''
| domain = [[Eukaryota]]
{{Taxobox_norank_entry | taxon = [[Unikonta]]}}
| regnum = [[Amoebozoa]]
| regnum_authority = [[Lühe]], 1913 ''emend.''
| subdivision_ranks = Subgroups
| subdivision = [[Slime mould|Mycetozoa]] (slime molds)
<br>[[Archamoebae]]
<br>[[Tubulinea]]
<br>[[Flabellinea]]
<br>Uncertain placement
<br> [[Acanthopodida]]
<br> [[Stereomyxida]]
<br> etc.
}}
The '''Amoebozoa''' are a major group of [[amoeboid]] protozoa, including the majority that move by means of
internal [[cytoplasm]]ic flow. Their [[pseudopod]]ia 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 mould]]s, [[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|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 (amoeba)|Chaos]]'' and
''[[Pelomyxa]]'' may be several millimetres in length, and some slime moulds cover several square feet.
== 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 [[vacuole]]s 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 [[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]].
Most Amoebozoa lack [[flagellum|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 [[gamete]]s. The flagella is generally anchored by a cone of microtubules, suggesting a close relationship to the [[opisthokont]]s. The [[mitochondrion|mitochondria]] characteristically have branching tubular [[crista]]e, but have been lost among archamoebae.
== Classification ==
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 [[percolozoa]]ns 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 [[eukaryote|eukaryotic]] evolution, as did most slime molds.
However, revised trees by [[Thomas Cavalier-Smith|Cavalier-Smith]] and Chao in 1996<ref>
{{cite journal | author=Cavalier-Smith, T. & Chao, E.E.
| title = Molecular phylogeny of the free-living archezoan ''Trepomonas agilis'' and the nature of the first eukaryote
| journal = Journal of Molecular Evolution
| year = 1996 | volume = 43 | pages = 551–562 | doi=10.1007/BF02202103
}}
</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>
{{cite journal | author=Cavalier-Smith, T.
| title = A revised six-kingdom system of life
| journal = Biological Reviews of the Cambridge Philosophical Society
| year = 1998 | volume = 73 | pages = 203–266
| doi = 10.1017/S0006323198005167}}
</ref> Studies based on other genes have provided strong support for the unity of this group.<ref>
{{cite journal | author = Baldauf, S.L. ''et al''.
| title = A kingdom-level phylogeny of eukaryotes based on combined protein data
| journal = [[Science (journal)|Science]]
| year = 2000 | volume = 290 | pages = 972–977
| doi = 10.1126/science.290.5493.972
| pmid = 11062127}}
</ref> [[David J. Patterson|Patterson]] treated most with the testate filose amoebae as the ramicristates<ref>
{{cite journal | author = David J. Patterson
| title = The Diversity of Eukaryotes
| journal = American Naturalist
| year = 1999 | volume = 145 | pages = S96–S124}}
</ref>, based on mitochondrial similarities, but the latter are now removed to the [[Cercozoa]].
Amoebae are difficult to classify, and relationships within the phylum remain confused. Originally the archamoebae and Mycetozoa were placed in a subphylum Conosa, which receives some support from molecular phylogenies, and the others were placed in a subphylum Lobosa, which is [[paraphyly|paraphyletic]]. Two major classes of Lobosa have been identified, the [[Tubulinea]] and [[Flabellinea]], but various others remain of uncertain placement. Strong similarities between Amoebozoa and [[Opisthokont]]s lead to the proposal that they form a clade called [[Unikont]]s.
On a broader scale, it appears (based in proteomes) that the amoebozoa form a [[stem group]] to animals and fungi, diverging from this lineage after it had split from the plants,<ref name=Eichinger2005>{{cite journal
| author = Eichinger, L.
| coauthors = Pachebat, J.A.; Glöckner, G.; Rajandream, M.A.; Sucgang, R.; Berriman, M.; Song, J.; Olsen, R.; Szafranski, K.; Xu, Q.; Others,
| year = 2005
| title = The genome of the social amoeba ''[[Dictyostelium]] discoideum''
| journal = Nature
| volume = 435
| issue = 7038
| pages = 43–57
| doi = 10.1038/nature03481
}}</ref>
as illustrated below:
{{phylogeny|Plants|Amoebozoa|Animals|Fungi}}
== List of amoeboid protozoa pathogenic to humans ==
*''[[Entamoeba histolytica]]''
*''[[Acanthamoeba]]''
*''[[Balamuthia mandrillaris]]''
== References ==
<references />
== External links ==
* [http://www.unige.ch/sciences/biologie/biani/msg/Amoeboids/Amoebozoa.html Molecular Phylogeny of Amoeboid Protists - Tree of Amoebozoa]
* [http://www.bairbrepaws.com/psneeley/FwrPLA.htm Joseph Leidy's Amoeba Plates]
[[Category:Protista]]
[[Category:Amoeboids]]
[[Category:Amoebozoa|*]]
[[ca:Amebozou]]
[[cs:Amoebozoa]]
[[de:Amoebozoa]]
[[es:Amoebozoa]]
[[et:Amoebozoa]]
[[ga:Amoebozoa]]
[[ja:アメーボゾア]]
[[ka:ამებები]]
[[lt:Ameboidiniai]]
[[nds:Amoebozoa]]
[[pl:Amoebozoa]]
[[sr:Amoebozoa]]
[[sv:Amöbor]]