Testate amoebae

Many amoeboid organisms have tests (shells) made out of organic or inorganic material. These can be smooth-walled, ornamented in different ways, or composed of smaller scales or subunits.

This page includes testate amoebae that have tubular pseudopodia, as well as those with filose pseudopodia. This is because empty tests (where the cell itself has died) can often be found, and with some familiarity be identified too.

Contents

Arcella
Centropyxis
Colichopodium
Difflugia cf. lobostoma
Other Difflugia
Trinema
Filose testate amoeba
“Rice-grain” test 
See also


Arcella

Amoeba with a round test that is flattened in profile, and with a single ventral aperture positioned centrally. In the images above, bridges of cytoplasm can be seen attached to the inside surface of the test, as well as contractile vacuoles.


Centropyxis

Test is brown-walled and covered in adhering particles. Distinguished by long spines which radiate outwards from it. There is a single circular aperture from which the cell extends its tubular pseudopodia. Empty tests are common and easily mistaken for other organic detritus.


Colichopodium

Easily mistaken for a naked amoeba, closer inspection shows that the cell surface is covered in a layer of fine scales, arranged in a regular pattern. The scales are most easily visible on the hyaline fringe of the pseudpodium which surrounds the cell as it moves. Electron microscopy has found that many apparently “naked” amoeba have such scales, but which are not visible to light microscopy. These cells have highly refractile bodies in the cytoplasm that may be crystalline. [Cell body about 25 µm across.]


Difflugia cf. lobostoma

Testate amoeba with a ovoid test, single terminal aperture, and lobose pseudopoda. The aperture has a “collar” with three lobes, visible when the opening faces the camera as the pseudopodia attach to the coverslip. Other Difflugia species may or may not have such collars, and have tests of different shapes. The test itself is made of scavenged material including sand grains and diatom frustules.


Other Difflugia

Another Difflugia with a similar mode of locomotion, and a test which is also made of scavenged material including diatom tests (visible in some of these images).

The cytoplasmic streaming and eruption of new pseudopodia during locomotion can be observed in this video below:


Trinema

The empty tests of this filose testate amoeba are common and easily recognized by the ventrally-placed aperture. The test is made of flat plates, which are circular or polygonal. The amoebae themselves have filose pseudopodia.


Filose testate amoeba

This organism had an egg-shaped, brown test with an aperture at one end. Pseudopodia were filose and branching, and when retracting sometimes had a kinked or wavy appearance; they emerged from the aperture. This sequence of images shows the cell sideways (showing the ovoid profile of the test) and later from end-on (circular profile) when the pseudopodia adhered to the slide.


“Rice-grain” test

These empty tests are made of small scales which are shaped like rice grains.


See also

Empty loricae of other organisms, such as the loricate ciliates may be confused with the empty tests of amoebae.

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