Shell of Difflugia acuminata: an agglutinated test made up of mineral particles glued together with secretions from within the cell
Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular amoeboidprotists, which differ from naked amoebae in the presence of a test that partially encloses the cell, with an aperture from which the pseudopodia emerge, that provides the amoeba with shelter from predators and environmental conditions.
The test of some species is produced entirely by the amoeba and may be organic, siliceous or calcareous depending on the species (autogenic tests), whereas in other cases the test is made up of particles of sediment collected by the amoeba which are then agglutinated together by secretions from within the cell (xenogenic tests). A few taxa (Hyalosphenidae) can build either type, depending on the circumstances and availability of foreign material.[1]
The assemblage referred to as "testate amoebae" is actually composed of several, unrelated groups of organisms. However, some features they all share that have been used to group them together include the presence of a test (regardless of its composition) and pseudopodia that do not anastomose.[2]
Testate amoebae can be found in most freshwater environments, including lakes, rivers, cenotes,[3] as well as mires and soils.
The strong and resistant nature of the tests allows them to be preserved long after the amoeba has died. These characteristics, along with the sensitivity that some species display to changes in environmental conditions (such as temperature, pH, and conductivity), has sparked their use as bioindicators and paleoclimate proxies in recent years.[4]
The following table includes a few examples of testate amoebae genera, and reflects their position within the classification by Adl et al. (2012),[7] where five supergroups (Amoebozoa, Opisthokonta, Excavata, SAR and Archaeplastida) were proposed to classify all eukaryotes. This classification purposefully avoids the use of Linnaean higher category names (phylum, class, order, family). While it has been noted that the names that Adl et al. provide for the clades may result confusing or uninformative regarding the relative degree of phenotypic distinctiveness amongst groups when used in isolation,[8] this system avoids creating superfluous ranks where unnecessary and provides stable group names that can be retained even when a group is moved to a different lineage, as is often the case with protists, as their classification remains in constant review.[7]
Traditionally, those species that form large networks of anastomosing pseudopodia, despite some of them having tests, are not counted amongst testate amoebae; this comprises genus Gromia and the Foraminifera (both in Rhizaria).[2]
Microworld - World of ameboid organisms - A database of both testate and naked amoebae with over 6,700 microphotographs and videos and over 1,700 species descriptions, as well as dichotomous and visual keys for identification.
^B., Scott, D. (2001). Monitoring in coastal environments using Foraminifera and Thecamoebian indicators. Medioli, F. S., Schafer, Charles T. Cambridge: Cambridge University Press. ISBN978-0521561730. OCLC70724931.{{cite book}}: CS1 maint: multiple names: authors list (link)
^ abKosakyan, Anush; Gomaa, Fatma; Lara, Enrique; Lahr, Daniel J.G. (2016). "Current and future perspectives on the systematics, taxonomy and nomenclature of testate amoebae". European Journal of Protistology. 55 (Pt B): 105–117. doi:10.1016/j.ejop.2016.02.001. hdl:11380/1302106. PMID27004416.
^Ralf Meisterfeld: Arcellinida, In: John J. Lee, Gordon F. Leedale, Phyllis Bradbury (Hrsg.): Illustrated Guide to the Protozoa, 2nd Edition. Vol. 2, Society of Protozoologists, Lawrence, Kansas 2000, ISBN1-891276-23-9, pp. 827-860
^Ralf Meisterfeld: Testate amoebae with filopodia , In: John J. Lee, Gordon F. Leedale, Phyllis Bradbury (Hrsg.): The Illustrated Guide to the Protozoa, 2nd Edition. Vol. 2, Society of Protozoologists, Lawrence, Kansas 2000, ISBN1-891276-23-9, pp. 1054-1084
