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Protozoa.
The Testate Amoebae. 
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  The Testate Amoebae.

Naked Amoebae Testate Amoebae

The testate amoebae produce shells, or tests, either by secreting them, as in the case of Euglypha, or by accreting them from appropriately sized particles encountered on their travels. The structural details of the test are the usual means of identifying them, along with whether their pseudopodia are lobose, In the form of smooth lobes. filose In the form of fine filaments. or reticulose. In the form of a network.


  Arcella.

Arcella is one of the most frequently encountered of the testate amoebae, especially in highly organically polluted waters, and in the sediments on the pond's bottom, where plant materials rot under conditions of low oxygen concentration. Others, such as Euglypha, Centropyxis and Difflugia are also common, but seem to require less polluted conditions.

Arcella group A number of testate amoebae of the genus Arcella are seen amongst decaying organic matter. The black masses are sulphide containing deposits typical of organic breakdown processes which take place under relatively anoxic conditions.
Brightfield: x200.
Two Arcella Two Arcella amongst decaying organic matter. A single pseudopodium (lobopodium) can be seen extending from the aperture in the test of the upper individual.
Annular brightfield: x400.
Arcella An Arcella moves among filaments of algae in a sample of decaying plant material in pond water. This picture shows a less polluted environment than the two pictures above.
Darkfield: x200.
Arcella Another Arcella from the same pond water sample as the above picture.
Darkfield: x400.
Arcella An unattatched Arcella drifting slowly through clear water. The aperture in the depressed underside of the test is clearly seen.
Darkfield: x300.


  Euglypha.

Euglypha. The testate amoeba Euglypha pulls itself along the surface of the microscope slide with its extended filipodia. The slide surface is sprinkled with bacterial cells. The test is not in focus as it trails behind the filipodia, raised up at an angle.
Phase Contrast: x600.
Euglypha. The testate amoeba Euglypha pulls itself along the surface of the microscope slide with its extended filipodia. The slide surface is sprinkled with bacterial cells. The test is not in focus as it trails behind the filipodia, raised up at an angle. The difference in colour compared to the picture above is due to the changed focus of the phase condenser.
Phase Contrast: x400.
Euglypha, test. Euglypha test. The amoeba has withdrawn inside the test, and can be seen contracted at the end opposite the opening.
Darkfield: x700.
Euglypha, test. This phase contrast picture of a somewhat flattened (and cracked) Euglypha test clearly shows the thin siliceous plates of which it is composed (see diagram).

These plates are produced and deposited in the outer layer of the amoeba's body, unlike other testate amoebae such as Difflugia, which build their test from found particles.
The nearby bacilli give scale to the picture.
Phase Contrast: x800.


  Centropyxis, etc.

Centropyxis. The test of the testate amoeba Centropyxis sp. It is not clear from this picture if the amoeba is "at home", or departed. This genus constructs its test from tiny quartz particles (sand grains).
Brightfield: x200.
Centropyxis. Another Centropyxis -- probably still inhabiting its test, or shell. When feeding, the amoeba extends a few lobopodia from the aperture in the test, but these are so difficult to see that close observation is needed to establish whether or not any given individual is alive.
Brightfield: x200.
Testate amoeba. This testate amoeba is possibly Difflugia corona, although the spines which are usually present in this species are nowhere to be seen.
Brightfield: x300.



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