A side view of the testate amoeba, Arcella.
The photo above is of what I believe is a testate amoeba from the genus Arcella. Testate amoebas are like normal amoebas, but are enclosed in a shell called a test. Towards the bottom of the cell is a single psuedopod, by which the amoeba achieves motility and apprehends its prey. The psuedopod extends from an aperture about the middle of the ventral side of the test, which is visible in the photo.
There are two types of tests in testate amoebas: Autogenic and xenogenic. Autogenic tests are composed of materials that the amoeba itself produced, and xenogenic tests are composed of materials that the amoeba collected (which sometimes includes diatoms). The test of Arcella is autogenic.
Amoebae can have many types of psuedopodia. The most familiar type is lobopodia, which are fat, thick psuedopods, as mentioned in a previous post. This amoeba, however, possessed what I believe are called filopodia. Filopodia are much slimmer than lobopodia. Of course, i’m not absolutely sure these are filopodia, as other amoebas possess axoneme (microtubule)-supported psuedopods called axopodia. Using a light microscope, it’s rather difficult to tell the difference. I supposed these were filopodia because a few of them look sort of wavy, and I would think that axopodia would be noticeably stiffer.
The amoebas had grown considerably since the last time I viewed the slide.
The term “amoeba” refers to any single cell (usually a protozoan, but sometimes photosynthesizers) that exhibits amoeboid movement. Amoeboid movement is the process by which a cell achieves motility by forming temporary extentions of its cell membrane and filling it with cytoplasm; this is known as a pseudopod, or “false foot”. The amoeba then adheres to a substrate (such as a glass microscope slide…) and pulls itself along.