Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular amoeboid 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 (Hyalospheniidae) can build either type, depending on the circumstances and availability of foreign material.
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.
Testate amoebae can be found in most freshwater environments, including lakes, rivers, cenotes, 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.
Possible fossils of testate amoebae have been found from the Gaoyuzhuang Formation, which is almost 1.6 billion years old. This would make them among the earliest known fossils of protists. Unusually, no other testate fossils are known until the Tonian, over 600 million years later.
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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),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, , pp. 827-860 and the filose Euglyphida (within the SAR supergroup),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, , pp. 1054-1084 although there are smaller groups that also include other testate amoebae.
Order Arcellinida
Family Arcellidae Arcella - Ehrenberg 1832 Antarcella - Deflandre 1928
Family Netzeliidae Netzelia - Ogden 1979
Family Hyalospheniidae Quadrulella - Cockerell 1909 Hyalosphenia - Stein 1859 Alocodera - Jung 1942 Apodera - Loeblich & Tappan 1961 Certesella - Loeblich & Tappan 1961 Porosia - Jung 1942 Nebela - Leidy 1874 Padaungiella - Lara & Todorov 2012
Family Microchlamyiidae Microchlamys - Cockerell 1911 Spumochlamys - Kudryavtsev & Hausmann 2007
Family Plagiopyxidae Bullinularia - Deflandre 1953 Geoplagiopyxis - Chardez 1961 Protoplagiopyxis - Bonnet 1962 Paracentropyxis - Bonnet 1960 Plagiopyxis - Penard 1910 Hoogenraadia - Gauthier-Lievre & Thomas 1958 Planhoogenraadia - Bonnet 1977
Family Cryptodifflugiidae Cryptodifflugia - Penard 1890 Wailesella - Deflandre 1928
Family Microcoryciidae Amphizonella - Greeff 1866 Diplochlamys - Greeff 1888 Microcorycia - Cockerell 1911 Penardochlamys - Deflandre 1953 Zonomyxa - Nusslin 1882 Parmulina - Penard 1902
Family Phryganellidae Phryganella - Penard 1902
Family Lamtopyxidae Lamtopyxis - Bonnet 1974
Family Distomatopyxidae Distomatopyxis - Bonnet 1964
Family Paraquadrulidae Paraquadrula - Deflandre 1932 Lamtoquadrula - Bonnet 1974
Family Centropyxidae Centropyxis - Stein 1857 Proplagiopyxis - Schonborn 1964
Family Trigonopyxidae Trigonopyxis - Penard 1912 Cyclopyxis - Deflandre 1929 Geopyxella - Bonnet & Thomas 1955 Cornuapyxis - Couteaux and Chardez 1981
Incertae sedis Argynnia - Vucetich 1974 Awerintzewia - Schouteden 1906 Cucurbitella - Penard 1902 Difflugia - Leclerc 1815 Geamphorella - Bonnet 1959 Heleopera - Leidy 1879 Jungia - Loeblich and Tappan 1961 Lagenodifflugia - Medioli & Scott 1983 Leptochlamys - West 1901 Lesquereusia - Schlumberger 1845 Maghrebia - Gauthier-Lievre & Thomas 1960 Mediolus - Patterson 2014 Microquadrula - Golemansky 1968 Oopyxis - Jung 1942 Pentagonia - Gauthier-Lievre & Thomas 1960 Physochila - Jung 1942 Pomoriella - Golemansky 1970 Pontigulasia - Rhumbler 1896 Protocucurbitella - Gauthier-Lievre & Thomas 1960 Pseudawerintzewia - Bonnet 1959 Pseudonebela - Gauthier-Lievre 1953 Pyxidicula - Ehrenberg 1838 Schoenbornia - Decloitre 1964 Schwabia - Jung 1942 Sexangularia - Awerintzew 1906 Suiadifflugia - Green 1975 Zivkovicia - Ogden 1987 Ellipsopyxis - Bonnet 1965 Ellipsopyxella - Bonnet 1975
Order Euglyphida
Family Euglyphidae Euglypha - Dujardin, 1841 Scutiglypha - Foissner and Schiller, 2001
Family Trinematidae Trinema - Dujardin 1841 Corythion - Taranek 1881 Puytoracia - Bonnet, 1970 Playfairina - Thomas 1961 Pileolus - Coûteaux and Chardez 1962
Family Sphenoderiidae Sphenoderia - Schlumberger 1845 Trachelocorythion - Bonnet 1979 Deharvengia - Bonnet 1979
Family Assulinidae Assulina - Leidy 1879 Placocista - Leidy 1879 Valkanovia - Tappan 1966
Family Cyphoderiidae Cyphoderia - Schlumberger 1845 Corythionella - Golemansky 1970 Campascus - Leidy 1879 Messemvriella - Golemansky 1973 Pseudocorythion - Valkanov 1970 Schaudinnula - Awerintzev 1907
Family Paulinellidae Paulinella - Lauterborn 1895 Ovulinata - Anderson, Rogerson & Hannah 1996 Micropyxidiella - Tarnawski & Lara 2015
Incertae sedis Pareuglypha - Penard 1902 Ampullataria - Van Oye 1956 Euglyphidion - Bonnet 1960 Heteroglypha - Thomas and Gauthier-Lièvre 1959 Tracheleuglypha - Deflandre 1928
Other Cercozoa
Family Chlamydophryidae Capsellina - Penard 1909 Lecythium - Hertwig and Lesser 1876 Rhogostoma - Belar 1921 Rhizaspis - Skuja 1948 Chlamydophrys - Cienkowsky 1876 Clypeolina - Cienkowsky 1877 Penardeugenia - Deflandre 1953 Leptochlamydophrys - Belar 1921 Diaphoropodon - Archer 1869
Family Pseudodifflugiidae Pseudodifflugia - Schlumberger 1845
Family Psammonobiotidae Alepiella - Golemansky 1970 Centropyxiella - Valkanov 1970 Chardezia - Golemansky 1970 Edaphonobiotus - Schönborn, Foissner & Meisterfeld 1983 Micramphora - Valkanov 1970 Micropsammella - Golemansky 1970 Nadinella - Penard 1902 Ogdeniella - Golemanski 1982 Psammonobiotus - Golemansky 1970 Propsammonobiotus - Golemansky 1991
Incertae sedis Feuerbornia - Jung, 1942 Frenzelina - Penard 1902 Lesquerella - Chardez and Thomas, 1980 Matsakision - Bonnet, 1967 Rhumbleriella - Golemansky 1970
Order Stramenopila
Family Amphitremidae Amphitrema - Archer 1869 Archerella - Loeblich and Tappan, 1961
Family Diplophryidae Diplophrys - Barker 1868
Family Amphifilidae Amphifila - Anderson and Cavalier-Smith 2012
Family Sorodiplophryidae Sorodiplophris - Dykstra and Olive 1975
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), 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, 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.
+AmoebozoaTubulineaArcellinidaArcellinaAmphizonella - Arcella - Microchlamys - Microcorycia - Spumochlamys DiffluginaBullinularia - Centropyxis - Difflugia - Distomatopyxis - Heleopera - Hyalosphenia - Lesquereusia - Nebela - Paraquadrula - Pontigulasia - Plagiopyxis - Quadrulella - Trigonopyxis PhryganellinaCryptodifflugia - Phryganella - WailesellaDiscoseaHimatismenidaCochliopodiumSAR SupergroupStramenopilaLabyrinthulomycetesAmphitremidaAmphitrema - ArcherellaRhizariaCercozoaThecofiloseaCryomonadidaRhizaspididaeCapsellina - Rhizaspis - RhogostomaVentricleftidaVentrifissura - VerrucomonasImbricateaSilicofiloseaEuglyphidaEuglyphidaeEuglypha - Scutiglypha AssulinidaeAssulina - Placocista - Valkanovia TrinematidaeCorythion - Playfairina - Puytoracia - Trinema CyphoderidaeCampascus - Corythionella - Cyphoderia - Messemvriella - Pseudocorythion - Schaudinnula.PaulinellidaeOvulinata - 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).
Notes The Thecamoebida (Amoebozoa), with the genus Thecamoeba, despite their name, do not have tests.
Euglyphid testate amoebae are closely related to the Foraminifera.
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
Bibliography
Medioli, F.S.; Scott, D.B.; Collins, E.; Asioli, S.; Reinhardt, E.G. (1999). The thecamoebian bibliography. Palaeontologia Electronica, 3: 1-161, . Medioli, F.S.; Bonnet, L.; Scott, D.B.; Medioli, B.E. (2003). The thecamoebian bibliography: 2nd edition. Palaeontologia Electronica, 61: 1-107, .