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Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular ameboid protists, 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]

Euglypha tuberculata, a species with a siliceous autogenic test.
The autogenic test of Arcella discoides, made up of organic plates.
Shell of Cyphoderia ampulla, composed of circular, siliceous plates produced by the amoeba.

Taxonomy and classification

Testate amoebae are a polyphyletic assemblage. The main testate amoebae groups are the lobose Tubulinea, which include Arcellinida, Difflugina and Phryganellina (within the Amoebozoa),[5] and the filose Euglyphida (within the SAR supergroup),[6] although there are smaller groups that also include other testate amoebae.[7]

Order Arcellinida

Order Euglyphida

Other Cercozoa

Order Stramenopila

Unclassified testate amoebae

    Paramphitrema Valkanov 1970

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]

Amoebozoa Tubulinea Arcellinida Arcellina Amphizonella - Arcella - Microchlamys - Microcorycia - Spumochlamys
Difflugina Bullinularia - Centropyxis - Difflugia - Distomatopyxis - Heleopera - Hyalosphenia - Lesquereusia - Nebela - Paraquadrula - Pontigulasia -

Plagiopyxis - Quadrulella - Trigonopyxis

Phryganellina Cryptodifflugia - Phryganella - Wailesella
Discosea Himatismenida Cochliopodium
SAR Supergroup Stramenopila Labyrinthulomycetes Amphitremida Amphitrema - Archerella
Rhizaria Cercozoa Thecofilosea Cryomonadida Rhizaspididae Capsellina - Rhizaspis - Rhogostoma
Ventricleftida Ventrifissura - Verrucomonas
Imbricatea Silicofilosea Euglyphida Euglyphidae Euglypha - Scutiglypha
Assulinidae Assulina - Placocista - Valkanovia
Trinematidae Corythion - Playfairina - Puytoracia - Trinema
Cyphoderidae Campascus - Corythionella - Cyphoderia - Messemvriella - Pseudocorythion - Schaudinnula.
Paulinellidae Ovulinata - Paulinella

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]

Notes

The Thecamoebida (Amoebozoa), with the genus Thecamoeba, despite their name, do not have tests.

Euglyphid testate amoebae are closely related to the Foraminifera.[9]

External links

  • 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.

References

  1. ^ B., Scott, D. (2001). Monitoring in coastal environments using Foraminifera and Thecamoebian indicators. Medioli, F. S., Schafer, Charles T. Cambridge: Cambridge University Press. ISBN 0521561736. OCLC 70724931. 
  2. ^ a b Kosakyan, Anush; Gomaa, Fatma; Lara, Enrique; Lahr, Daniel J.G. "Current and future perspectives on the systematics, taxonomy and nomenclature of testate amoebae". European Journal of Protistology. 55: 105–117. doi:10.1016/j.ejop.2016.02.001. 
  3. ^ Sigala, Itzel; Lozano-García, Socorro; Escobar, Jaime; Pérez, Liseth; Gallegos-Neyra, Elvia (2016-06-28). "Testate Amoebae (Amebozoa: Arcellinida) in Tropical Lakes of Central Mexico". Revista de Biología Tropical. 64 (1): 377–397. doi:10.15517/rbt.v64i1.18004. ISSN 2215-2075. 
  4. ^ Mitchell, Edward A. D.; Charman, Daniel J.; Warner, Barry G. (2008-08-01). "Testate amoebae analysis in ecological and paleoecological studies of wetlands: past, present and future". Biodiversity and Conservation. 17 (9): 2115–2137. doi:10.1007/s10531-007-9221-3. ISSN 0960-3115. 
  5. ^ 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, ISBN 1-891276-23-9, pp. 827-860
  6. ^ 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, ISBN 1-891276-23-9, pp. 1054-1084
  7. ^ a b c Adl, Sina M.; Simpson, Alastair G. B.; Lane, Christopher E.; Lukeš, Julius; Bass, David; Bowser, Samuel S.; Brown, Matthew W.; Burki, Fabien; Dunthorn, Micah (2012-09-01). "The Revised Classification of Eukaryotes". Journal of Eukaryotic Microbiology. 59 (5): 429–514. doi:10.1111/j.1550-7408.2012.00644.x. ISSN 1550-7408. 
  8. ^ Ruggiero, Michael A.; Gordon, Dennis P.; Orrell, Thomas M.; Bailly, Nicolas; Bourgoin, Thierry; Brusca, Richard C.; Cavalier-Smith, Thomas; Guiry, Michael D.; Kirk, Paul M. (2015-04-29). "A Higher Level Classification of All Living Organisms". PLOS ONE. 10 (4): e0119248. doi:10.1371/journal.pone.0119248. ISSN 1932-6203. 
  9. ^ Testate amoebae as environmental indicators (PDF) 

Bibliography

  • Medioli, F.S.; Scott, D.B.; Collins, E.; Asioli, S.; Reinhardt, E.G. (1999). The thecamoebian bibliography. Palaeontologia Electronica, 3: 1-161, [1].
  • Medioli, F.S.; Bonnet, L.; Scott, D.B.; Medioli, B.E. (2003). The thecamoebian bibliography: 2nd edition. Palaeontologia Electronica, 61: 1-107, [2].