Testate amoebae

Shell of Cyphoderia ampulla, composed of circular, siliceous plates produced by the amoeba.

Overview

Testate amoebae (Testacea, or Hyalosphenia) are amoeboid protists, differing from naked amoebae in that they inhabit a test, or shell. The test of the testate can be created entirely by the amoeba, in which it would create an organic, siliceous, or calcareous shell depending on the species of testate amoeba. These tests created entirely by the amoeba are known as autogenic tests, as seen in Figure 1. An xenogenic test is made up of particles of sediment collected by the amoeba which are then agglutinated together by secretions within the cell, as seen in Figure 2.

Figure 1: the autogenic test of Arcella discoides, made up of organic plates..

Figure 2: An xenogenic test of a Difflugia acuminata. Depicts an agglutinated test made up of mineral particles glued together with secretions from within the cell.

Significance

The shells which these protozoa develop are able to be preserved long after the amoeba has died. This characteristic combined with Testacea sensitivity to environmental factors, such as pH, temperature, etc., has shown their usefulness as bioindicators and paleoclimate proxies.

Habitat

This group of free-living microorganisms inhabit aquatic to moist habitats including: estuaries, lakes, rivers, wetlands, soils, litter, and moss habitats. They are able to live in both fresh and marine water, however, compared to naked amoeba, testate amoebae are less abundant in most soils. They thrive in soil environments that are moist and within forested systems.

References

[1] Coleman, D.J., Callaham, M. A., Jr., Crossley, D.A.. November 2017. 'The Fundamentals of Soil Ecology'. Third Edition. Elsevier Academic Press.

[2] Louiser, J.D., Parkinson, S.S.. 1981. 'Evaluation of a membrane filter technique to count soil and litter Testacea'. Soil Biol. Biochem. 13. 209-2013

[3] Mitchell, Edward A. D.; Charman, Daniel J.; Warner, Barry G. 2008. "Testate amoebae analysis in ecological and paleoecological studies of wetlands: past, present and future" (PDF). Biodiversity and Conservation. 17 (9): 2115–2137. doi:10.1007/s10531-007-9221-3. ISSN 0960-3115.