Testacea

Testate amoebae (Amoebozoa) are small shell or test-bearing, single-celled organisms (shell lengths: 0.005 - 0.6 mm), common to all aquatic and moist, terrestrial environments. In streams,w wetlands and lakes, testates often represent one of the highest number of species of any faunal group, reaching considerable benthic densities1-3. Locomotion and food capture is by pseudopodia of varied 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. Testate amoebae serve as food-source for a variety of benthic meio- and macrofaunal species, linking to the aquatic food-web4.
The spatial distribution of testates is determined largely by the pore spaces of streambed-sediment interstices or soil/leaf-litter environments. In moist soils, shell size largely declines with increasing soil depth5. Testates tolerate a wide temperature range, occurring with many cosmopolitan species from the polar regions to the tropics. Testate amoebae are used as 'proxis' of climate change, habitat destruction and organic pollution.
Species are best assessed using living specimens, because empty shells deposited in the sediments remain intact for long periods. The shell morphology, the shell and aperture size and the pseudopodial morphology are essential for taxonomic characterization.