Testate amoebae

Testate amoebae are small shell or test-bearing (shell lengths: 5 - 400 μm), single-celled ameboid organisms, composed of several unrelated groups. These testates are common to all aquatic and moist, terrestrial environments. The tests of many species are often composed of aglutinated mineral particles, but other species are characterized by siliceous autogenic tests or tests made of organic plates.

• In all freshwater systems, testates often represent one of the species-richest invertebrate group, reaching considerable densities1-3.
• Locomotion and food capture is by pseudopodia of varied and sometimes complex morphology. Testates display a wide range of feeding habits, with species preying on other uni- and multicellular organisms, bacteria, microfungi, algae and particulate organic matter.
• The spatial distribution of testates is determined largely by physical and chemical parameters such as pH, conductivity and the pore spaces of the interstitial sediments or soil/leaf-litter environments. In moist soils, shell size largely declines with increasing soil depth3. In streambed sediments, the densities of testate species are inversely related to their body mass1.
• Testates are represented by many cosmopolitan but also endemic species and tolerate a wide temperature range, occurring from the polar regions to the tropics.
• Species are best assessed using living specimens, because empty shells deposited in the sediments remain intact for several weeks. The shell morphology, the shell and aperture size and the pseudopodial morphology are essential for species or species group identification.