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Testate amoebae (or thecamoebians, Arcellinida[1] or lobose testate amoebae[2]) are single-celled protists partially enclosed in a simple test (shell).
They are commonly found in soils, leaf litter, peat bogs and near/in fresh water. [1]
Almost all testate amoebae reproduce asexually via binary fission. A sexual component to reproduction has not yet been found. Testate amoebae move by using pseudopodia (false feet), a temporary cell extension used for moving, and taking in food.
Testate amoebae taxa are differentiated by their test characteristics and what kind of pseudopodia they have (lobose, recticulose, or filose).
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Test/shell
Simple tests (or shells) are be made by either secretion (autogenous tests) or by the agglutination of foreign material (xenogenous tests), or sometimes a combination of both. Past environmental changes can be determined by analysing the composition of fossil tests, including the reconstruction of past climate change.[1]
Evolutionary history
Fossils of testate amoebae date back to the Cryogenian period.[3] Testate amoebae are theorized to be mostly polyphyletic (coming from more than one ancestral type), but testaceafilosea, one group of testate amoebae, are theorized to be made up of one ancestral type (monophyletic). Ancient tests of terrestrial fauna are commonly found in fossilized amber [4], although an important new study has found mid-Cretaceous testate amoeba (i.e., Diffligia, Cucurbitella) in ancient lake sediments [5]. It is likely that the group has evolved minimally over the course of the Phanerozoic.
References
- ^ a b c http://www.microscopy-uk.org.uk/mag/artjun03/gsamoebae.html Testate amoebae, peat bogs and past climates. accessed 16 march 2007
- ^ Lara E, Heger TJ, Ekelund F, Lamentowicz M, Mitchell EA (April 2008). "Ribosomal RNA genes challenge the monophyly of the Hyalospheniidae (Amoebozoa: Arcellinida)". Protist 159 (2): 165–76. doi:. PMID 18023614. http://linkinghub.elsevier.com/retrieve/pii/S1434-4610(07)00071-5.
- ^ Porter, S.A., and Knoll, A.H. (2000) Testate amoeba in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon: Paleobiology 26 (3): 360-385. Also see Cryogenian
- ^ Schmidt, A.R., Ragazzi, E., Coppellotti, O., Roghi, G. (2006) A microworld in Triassic amber, Nature, v. 444 (14):835.
- ^ van Hengstum, P.J., Reinhardt, E.G., Medioli, F.S., Grocke, D.R. (2007) Exceptionally preserved late albian (Cretaceous) Arcellaceans (Thecamoebians) from the Dakota Formation near Lincoln, Nebraska. Journal of Foraminiferal Research 37(4): 300-308
See also
External links
- Tree of Life: Arcellinida
- An article by G. T. Swindles
- Protozoa: The testate amoebae
- BioImages: The Virtual Field-Guide (UK) - TESTACEA (Testate amoebae)
- Pictures of testate amoebae
- The Cushman Foundation Thecamoebian Page
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