Testate amoebae

Testate amoebae (Protozoa: Rhizopods) are single-celled protists partially enclosed in a simple test (shell). [ http://www.microscopy-uk.org.uk/mag/artjun03/gsamoebae.html Testate amoebae, peat bogs and past climates. accessed 16 march 2007] Other names for the group include Thecamoebians, Arcellaceans (after the a large group of lacustrine testate amoeba), and sometimes Rhizopods.

They are commonly found in soils, leaf litter, peat bogs and near/in fresh water. [ http://www.microscopy-uk.org.uk/mag/artjun03/gsamoebae.html Testate amoebae, peat bogs and past climates. accessed 16 march 2007]

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).

Test/shell

Simple tests (or shells) are be made by either secretion (autogenous tests) of a 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. [ http://www.microscopy-uk.org.uk/mag/artjun03/gsamoebae.html Testate amoebae, peat bogs and past climates. accessed 16 march 2007]

Evolutionary history

Fossils of testate amoebae date back to the Cryogenian period. [ 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 [http://www.palaeos.com/Proterozoic/Neoproterozoic/Cryogenian/Cryogenian.2.html Cryogenian] ] Testate amoebae are theorized to be mostly polyphyletic (coming from more than one ancestral type), but testaceafilosea, another 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 [Schmidt, A.R., Ragazzi, E., Coppellotti, O., Roghi, G. (2006) A microworld in Triassic amber, Nature, v. 444 (14):835. ] , although an important new study has found mid-Cretaceous testate amoeba (i.e., "Diffligia", "Cucurbitella") in ancient lake sediments [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] . It is likely that the group has evolved minimally over the course of the Phanerozoic.

References

ee also

*Foraminifera

External links

* [http://tolweb.org/Arcellinida/124471 Tree of Life: Arcellinida]
* [http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artjun03/gsamoebae.html An article by G. T. Swindles]
* [http://www.micrographia.com/specbiol/protis/homamoeb/amts0100.htm Protozoa: The testate amoebae]
* [http://www.bioimages.org.uk/HTML/T133652.HTM Bio
]
* [http://zbip.one.pl/photogallery.php?album=4 Pictures of testate amoebae]
* [http://www.cushmanfoundation.org/resources/slides/thecamo.html The Cushman Foundation Thecamoebian Page]