Here's another interesting organism that lives in the temporary pools of water, known as phytotelmata, that accumulate in cavities in the surface roots of beech trees. It's a testate rhizopod - an amoeba that lives in a shell that it secretes - and is called Arcella. It's about a tenth of a millimetre in diameter. The shell in old specimens tends to be brown but this one is nicely translucent, revealing the exquisite sculptured pattern that decorates its surface.
Here's the flip-side, showing the hole in the underside of the hollow do-nut shaped shell and...
... here, with a shift in focus, you can see the amoeba inside, with one arm or pseudopodium protruding out of the hole. The dark structure that you can see in the cytoplasm is a vacuole filled with carbon dioxide - the organism produces one of these to increase its buoyancy when it needs to float up to the surface.
Here you can see the whole organism inside the shell in side view, poised above the hole. The circular structure in the cytoplasm, top left at about 10 o'clock, is a nucleus.... the control centre of the cell.
There are always two nuclei in the cytoplasm of each Arcella.... so which one is in control? Who knows?
And finally, here it is on the move, extending a pseudopodium that it uses for locomotion and food capture.
This is probably Arcella discoides. If you'd like to see some wonderful illustrations of more testate rhizopods take a look at this page, where you'll need to double-click on the images to enlarge them.