Identification key for Holocene Lacustrine Arcellacean (Thecamoebian) taxa
Article number: 1.1.4A
Copyright Palaeontological Assocation, 28 January 1998
Plain-language and multi-lingual abstracts
Submission: 10 November, 1997. Acceptance: 7 January, 1998
Arcellaceans (thecamoebians), predominantly freshwater protozoans, have been studied for over a century. However, in the last ten years their usefulness as paleoenvironmental indicators has become better understood because researchers have recognized that certain morphotypes (strains) prefer distinct microenvironments. Unfortunately, the monoclonal nature and simple morphorphology of the group has led to considerable taxonomic confusion, threatening their utility in paleolimnological research. This key was created to help new researchers studying the group, and to standardize the taxonomy.
Arun Kumar and Andrew P. Dalby. Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, CANADA K1S 5B6
KEY WORDS: thecamoebian(s), arcellacean(s) Holocene, identification key
Final citation: Kumar, Arun and Dalby, Andrew P. 1998. Identification key for Holocene Lacustrine Arcellacean (Thecamoebian) taxa, Palaeontologia Electronica Vol. 1, Issue 1; 4A; 34p. https://doi.org/10.26879/98004
Arcellaceans (thecamoebians) are clonal, predominantly freshwater protozoans, although they can also occur in brackish water environments and moist soils (Medioli and Scott 1983). They can be found in a wide range of geographic settings, ranging from tropical to arctic latitudes (Nair and Mukherjee 1968; Green 1975; Dallimore et al. 1997). These organisms have an amoebid sarcodine cell with pseudopods and a simple sac-like test, either flattened or rounded with an aperture located on or near the tapered end, or a beret-shaped test with an invaginated aperture on the ventral side which is more or less flattened. A substantial amount of morphological variability has been observed among these two broad groups.
A few forms like Lagenodifflugia and Pontigulasia appear to have a second chamber consisting of an enlarged collar separated from the rest of the test by a distinct constriction (Medioli and Scott 1988; Medioli et al. 1990). Tests are either secreted (autogenous), or agglutinated (xenogenous) with sand particles or diatom frustules (xenosomes) in autogenous cement. Autogenous tests are usually smooth, proteinaceous, sometimes made of siliceous platelets (idiosomes), or rarely calcareous. (See Medioli et al. 1990, for a review of fossil arcellaceans).
Arcellacean tests do not demonstrate a high degree of morphological diversity, but important taxonomic characteristics include (Asioli et al. 1996): presence or absence of spines; nature and shape of xenosomes and idiosomes; shape and composition of tests; and morphological features associated with the apertures, such as diaphragms, collars, lobes, and teeth.
Test size can vary between 50 to 300 um or even greater, thus it is of no taxonomic importance as it is determined at the time of fission by the volume of cytoplasm available in the parent test (Medioli and Scott 1983). Cytoplasmic volume is in turn probably controlled by the availability of food in the period preceeding reproduction (Medioli et al. 1990).
It has long been known that various arcellacean species preferentially inhabit specific environments. Rcent research has determined that some infrasubspecific variants (strains) are particularly sensitive to environmental variations (Asioli et al. 1996; Patterson et al. 1996; Reinhardt et al. 1998). In particular, arcellaceans have proven to be useful tools in assessing remediation rates within industrially polluted settings (Asioli et al. 1996; Patterson et al. 1996; Reinhardt et al. 1998).
Unfortunately, the subtle criteria used to differentiate the rather simple arcellacean morphologies, and confusion over the proliferation of taxonomic names during the last hundred years has limited their utility (Medioli and Scott 1983). In this paper, we present a taxonomic key designed to:
- illustrate the various morphologies that we find useful in paleolimnological research and;
- provide an arcellacean identification guide for future researchers engaged in paleolimnological research.
Taxa illustrated in this key are from Crosswise and Peterson lakes, near Cobalt, Ontario; Swan Lake, north of Toronto, Ontario; Lake Erie, Ontario; and Lake Orta, northern Italy. Exact sample locations are provided with individual illustrations.
|Key Position: 1|
|1a. Test circular, hemispherical to ovoid; made of proteinaceous matter and agglutinated grains.||1b. Test ovoid, pyriform, elongate to acuminate; made of agglutinated mineral grains or diatom frustules.|
Archer, W. 1866.Quarterly Journal of Microscopical Science, new series, 6:185-188.
Asioli, A., Medioli, F.S., and Patterson, R.T. 1996. Thecamoebians as a tool for reconstruction of paleoenvironments in some Italian lakes in the foothills of the southern Alps (Orta, Varese and Candia). Journal of Foraminiferal Research, 26:248-263.
Carter, H.J. 1856. Notes on the freshwater Infusoria of the island of Bombay. No. 1. Organization. Annals and Magazine of Natural History, series. 2, 18(105):221-249.
Carter, H.J. 1864. On freshwater Rhizopoda of England and India. Annals and Magazine of Natural History, series 3, 13:18-39.
Cash, J., and Hopkinson, J. 1905. The British freshwater Rhizopoda and Heliozoa. Vol. I: Rhizopoda, part 1. Ray Society, London.
Cash, J., and Hopkinson, J. 1909. The British freshwater Rhizopoda and Heliozoa. Vol. II: Rhizopoda, part 2. Ray Society, London.
Dallimore, A., Schröder-Adams, C.J., and Burn, C.R. 1997. Environmental control on thecamoebian assemblages in lakes on Richards Island, MacKenzie Delta, N.W.T. Geological Association of Canada-Mineralogical Association of Canada Annual Meeting May 19-21, 1997, Abstract Volume, A34
Deflandre, G. 1929. Le genre centropyxis Stein. Archiv fur Protistenkunde, 67:323-375.
Ehrenberg, C.G. 1830. Organisation, systematik und geographisches Verhältnis der Infusionsthierchen. Druckerei der Königliche Akademie der Wissenschaften, Berlin.
Ehrenberg, C.G. 1832. Über die Entwicklung und Lebensdauer der Infusionsthiere, nebst ferneren Beiträgen zu einer Vergleichung ihrer organischen Systeme. Königliche Akademie der Wissenschaften zu Berlin Physikalische Abhandlungen, 1831, 1-154.
Ehrenberg, C.G. 1840. Das grössere Infusorienwerke. Königliche Preussischen Akademie der Wissenschaften zu Berlin Bericht, 198-219.
Ehrenberg, C.G. 1843. Verbreitung und Einfluss des mikroskopischen Lebens in Süd-und Nord Amerika. Königliche Akademie der Wissenschaften zu Berlin Physikalische Abhandlungen, 1841, 291-446.
Ehrenberg, C.G. 1848. Fortgesetzte Beobachtungen über jetzt herrschende atmospharische mikroskopische Verhaltnisse. Bericht uber die zur Bekanntmachung geeigneten Verhandlungen der Koniglichen Preussischen Akademie der Wissenschaften zu Berlin, 13:370-381.
Ehrenberg, C.G. 1872. Nachthrag zur Übersicht der organischen Atmosphärilien. Kšnigliche Akademie der Wissenschaften zu Berlin Physikalische Abhandlungen, 1871, 233-275.
Green, J. 1975. Freshwater ecology in the Mato Grosso, Central Brazil, IV: Associations of testate Rhizopoda. Journal of Natural History, 9:545-560.
Haman, D. 1982. Modern Thecamoebinids (Arcellinida) from the Balize Delta, Louisiana. Transactions of the Gulf Coast Association of Geological Societies, 32:353-376.
Hempel, A. 1898. A list of the Protozoa and Rotifera found in the Illinois River and adjacent lakes at Havana, Ill. Illinois State Laboratory of Natural History Bulletin, 5:301-388.
Lamarck, J.B. 1816. Histoire naturelle des animaux sans vertebres. Verdiere, Paris, 2:1-568.
Leidy, J. 1874. Notice of some new fresh-water rhizopods. Proceedings of the Academy of Natural Sciences of Philadelphia, series 3:77-79.
Leidy, J. 1879. Fresh water rhizopods of North America. United States Geological Survey of the Territories Report, 12:1-324.
Medioli, F.S., Scott, D.B., and Abbott, B.H. 1987. A case study of protozoan interclonal variability: taxonomic implications. Journal of Foraminiferal Research, 17:28-47.
Medioli, F.S., and Scott, D.B. 1983. Holocene Arcellacea (Thecamoebians) from eastern Canada. Cushman Foundation For Foraminiferal Research Special Publication 21.
Medioli, F.S., and Scott, D.B. 1988. Lacustrine thecamoebians (mainly arcellaceans) as potential tools for paleolimnological interpretations. Paleogeography, Paleoclimatology, Paleoecology, 62:361-386.
Medioli, F.S., Scott, D.B., Collins, E.S., and McCarthy, F.M.G. 1990. Fossil thecamoebians: present status and prospects for the future. In Hemleben, C., Kaminski, M.A., Kuhnt, W. and Scott, D.B., (eds.), Paleoecology, Biostratigraphy, Paleoceanography and Taxonomy of Agglutinated Foraminifera, North Atlantic Treaty Organization Advanced Study Institute Series, Series C. Mathematical and Physical Sciences, 327:813-840.
Nair, K.N., and Mukherjee, R.N. 1968. On some testacean rhizopods (Protozoa: Sarcodina) of the ground and tree mosses from Calcutta and its environs. Proceedings of the National Academy of Sciences of India, 38B:185-193.
Ogden, C.G., and Ellison, R.L. 1988. The value of the organic cement matrix in the identification of the shells of fossil testate amoeba. Journal of Micropalaeontology, 7: 233-240.
Ogden, C.G., and Hedley, R.H., 1980. An Atlas of Freshwater Testate Amoeba. British Museum (Natural History), Oxford University Press.
Patterson, R.T., MacKinnon, K.D., Scott, D.B., and Medioli, F.S. 1985. Arcellaceans (Thecamoebians) in small lakes of New Brunswick and Nova Scotia: modern distribution and Holocene stratigraphic changes. Journal of Foraminiferal Research, 15:114-137.
Patterson, R.T., Barker, T. and Burbidge, S.M. 1996. Arcellaceans (thecamoebians) as proxies of arsenic and mercury contamination in northeastern Ontario lakes. Journal of Foraminiferal Research 26:172-183.
Penard, E. 1890. Études sur les Rhizopodes d'eau douce. Mémoires de la Société de Physique et d'Histoire Naturelle de Genève, 31(2), 1-230.
Penard, E. 1899. Les Rhizopodes de faune profonde dans le lac Léman. Revue Suisse de Zoologie, 7, 1-142.
Penard, E. 1902. Faune Rhizopodique du Bassin du Lèman. Henry Kundig, Genve.
Penard, E. 1905. Les Sarcodines des grands lacs. Henry Kundig, Genève.
Perty, M. 1849. Über vertikale Verbreitung mikroskopischer Lebensformen. Naturforschende Gesellschaft in Bern Mittheilungen, 153-176.
Reinhardt, E.G., Dalby, A.P., Kumar, Arun, and Patterson, R.T. 1998. In press. Utility of arcellacean phenotypic variants as pollution indicators in mine tailing contaminated lakes near Cobalt, Ontario, Canada. Micropaleontology 43(3).
Scott, D.B., and Medioli, F.S., 1983. Testate rhizopods in Lake Erie: modern distribution and stratigraphic implications. Journal of Paleontology, 57:809-820.
Wallich, G.C. 1864. On the extent, and some of the principal causes, of structural variation among the difflugian rhizopods: Annals and Magazine of Natural History, series 3, 13:215-245.