The testate amoeba (“test” means shell) is one of the single celled creatures we commonly find while looking at soil in the microscope. It’s a type of protozoa, just like regular amoebae, but it lives in a shell like a snail. Some eat bacteria, algae, or other protozoa, and some live on decaying organic material. As with all soil protozoa, they live in the thin film of water that surrounds soil particles.
We normally see them like this (photos from my phone):
They can come in many different shapes and sizes. Some have beautiful scale patterns on the shell, some have spiked shells, some are just smooth and simple. As with any soil creatures, people who aren’t used to looking at things in a microscope often have difficult putting them into perspective. I purposely painted this one looking and moving like a snail to hopefully make it easier to relate to.
It’s extremely rare for us to see the actual body of the amoeba, which is why I painted the shell to be more prominent than the amoeba itself. I’ve been looking at soil and water samples in microscopes since 2011. In that time I’ve seen literally thousands of testate amoebae and I think I’ve seen them coming out maybe three times.
There was exactly one time that I actually saw a very small one moving around in a soil sample, and I was super lucky to catch a video of it with my phone. Here is a link to the video. This is the only time I’ve ever seen one like this. Normally the ones we see are like the photos above, and they are sitting still.
The amoeba extends what are called “pseudopods” (pseudo=fake, pod=feet). You might already know that amoebae are shapeless creatures that move by flowing and changing form. They can stretch their bodies out to form pseudopods and use them to move, anchor themselves, or catch food. They can create many of these fake feet at once, and they can be thick and globby or thin filaments like hairs. Watching an amoeba move around is one of the most fascinating things I’ve ever seen. It looks exactly like a glass of milk or some liquid soap that spilled on the floor, then started crawling around. Sort of a creepy image but that’s really how it looks. They move slowly and watching them can be mesmerizing.
Naked amoebae are difficult to spot because they are usually completely clear with only a faint outline and some inner contents of the cell visible, and the distinct movement giving us a clue to its presence. If disturbed I imagine they would squeeze themselves into the nearest crevice like a clump of soil to hide, which is why it’s rare for us to see them at all. Testate amoebae are easy to spot because of the shell, but since they can withdraw and hide inside their shell it’s extremely difficult to see the amoeba itself. That makes it hard to tell if anyone is home or if it’s just an empty shell.
We see these creatures in the highest numbers in forest soils and some composts, but they can be common in garden and agricultural soils as well. It is very rare for us to have a soil sample that doesn’t have at least one testate amoeba in it.
This is the second piece in my soil life series of paintings which try to show microscopic animals in a way that is more familiar.