by Wim van Egmond, The Netherlands
Arcella gibbosa, its test is about 0.1 mm. in diameter.
important group of amoeba make a protective shell called a 'test'. These
shelled amoebas can be collected with the same methods as 'naked amoeba'
Some caution must be taken when examining them since the tests easily break.
I always add some dots of Vaseline under the corners of the cover slip.
It often takes some minutes before disturbed shelled amoeba become active
The image shows how the shelled amoeba Arcella is attached to its house by thin pseudopods. Bigger pseudopods are extended through the small opening at the bottom of the test.
amoeba of the genus Arcella make delicate tests. When observed with
a high power objective (40X), the fine texture of the test can be seen.
They construct their test by glueing tiny bits of inorganic detritus together.
The bottom image shows the much cruder design of Difflugia, another common shelled amoeba. The sand particles that are used, obscure the view, so the living cell of the amoeba can only be observed when it extrudes its pseudopods.
Difflugia, its test is about 0.3 mm. long.
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