Microscopic Living Do-nut

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.

Teeming Millions - Paramecium Population Explosion

Well, teeming thousands anyway. These little organisms are Paramecium, single-cells protists that swim with incredible speed using ciliary hairs on their surface, that beat in rhythm. Here they're magnified one hundred times. This single drop of  water on a microscope slide probably contained about five hundred...

... and this little pool of water, trapped in a cavity formed by the coalesced roots of a beech tree, must have contained millions, feeding in bacteria and other microscopic organisms that were in turn feeding on the rotting leaves trapped in the water. The pool is fed by rivulets of water that trickle down the trunk when it rains. Temporary pools of water trapped in plants like this are known as phytotelmata. The best-known examples are the pools of water trapped by the leaves of bromeliads (urn plants) that grow as epiphytes in the rainforest tree canopy. They host all sorts of exotic animals - tree frogs, land crabs, dragonflies - but this beech tree-root equivalent hosted nothing larger than rat-tailed maggots - the larval stages of drone flies. But while the species diversity in the beech-tree pool might have been low, the sheer abundance of the Paramecium was staggering. 

Here they are magnified two hundred times. The circles that you can see in some of them are contractile vacuoles, that constantly expell water from the cell cytoplasm.

  

At 400 times magnification you can see the fine cilia (top right) that are arranged in rows over the surface of the cell - you can just make out their dark parallel lines and you can also see algae that the Paramecium has ingested, inside the cell.

Static images don't really do justice to the helter-skelter movement of these little protists, but the video clip below gives some impression of what is going on in those little temporary pools of water trapped by the tree roots.