I try to capture my thoughts when I observe an organism in the microscope for the first time. I usually keep these notes private, but have decided to share my awe, wonder and questions when first observing an Arcella last year. What goes through your mind when you see something interesting for the first time?
The observation
A simple moss squeeze from roof fallen moss on a mild February day last year (high 9 degrees Centigrade). One drop of the moss squeeze solution.
What I observed
I have selected a small piece of moss that has fallen from the roof or my home on a mild February afternoon. The moss sample is sodden and water drips from it as I pick it up. The outside temperature is about nine degrees Centigrade, so there’s a good chance of a lot of activity in the little moss pad. I never know exactly what I am going to find, and in these early days of exploration, almost everything is a novelty.
The microscope is already attached to the digital camera that feeds directly into my lap top screen. I have taken to observing through the camera, rather than through the eyepiece of the microscope. I agitate the moss with a wooden tooth pick and then squeeze out the moisture into a filter paper in a funnel. Just as the final couple of millilitres of unfiltered moss squeeze remains, I suck up the concentre into a plastic Pasteur pipette.
Under the x4 objective, among the other debris, there is a small rich brown disc measuring nine millimetres in diameter on my screen, approximately 75 micrometres (Figure 1) . Easy to pass by, but it does catch my attention by its seemingly perfect dark circle, with a lighter circle in the centre: I’m curious. Too regular to be a bit of debris, though if something bigger and moving was nearby I would have most likely overlooked it. On adjusting the intensity of the light under it, the disc changes into a rich, red and orange brown, with clearly more to it: an indication of a texture.
I switch up to the next objective, x10. After the mechanical click, followed by adjustment of the light from beneath, the circle now becomes 24 millimetres in diameter on my screen (Figure 2). Incredibly, I think I can see movement within the disc, or maybe it’s just the focusing of the light. Increasing the light intensity enriches the colours further. I hold the focus steady and let the view settle. A clear bubble appears on the circumference, a distortion of the light. There seems to be movement within the structure, like bubbles collapsing slowly. A small protrusion catches the light, like a hand of a clock ticking around the inner circumference. Stopping, to pick up again further around the circumference. Then one of the clock hands extends, like a transparent finger a millimetre away from the circumference into the water surrounding it. It grows, with a light greenish tinge. Reaching four times it’s length, it waves back and forth before retracting. This is more than the trick of the light. Is there something stuck under this disc, or is it an organism itself?
Time for the next objective, my dry lens at x40. The full detail of the disc comes into view in chromatic light, then with adjustment of the condenser and light intensity it settles to pastels (Figure 3). There is an outer crust that is light brown and textured, then what looks like a lighter irregular circle within the crust. There are gentle pulsing movements within and then I see it. A tentacle stretches out from under the case. It has a greenish tinge due to the refraction of light at a high magnification. Then another, nearby, less regular in shape, but a protrusion none the less. The tentacles move out slowly, with a determined searching, but their covering disc remains stationary.
It reminds me of how I imagined John Wyndham’s science fiction sea creatures in the Kraken Wakes as they came from the depths onto the land. With a hard armoured shell under which tentacles protrude, they harvest humans using biological land tanks. Their soft delicate bodies protected by hard shells (Figure 4).
As I sit back and observe the screen, I can’t help but to compare the image to that of a distant moon, rocky and pock marked. But then after a while, as it almost glows in the under increased lighting, it conjures up NASA images of the Sun (Figure 5). The slowly churning molten surface, with dark spots of activity, and then from the edges, solar flares leaving the surface, similar to the protrusions from this flat, amoebic creature. Strange how I compare the very small with the very large.
Watching more closely, I think I can make out regular oblong shapes of diatoms within the shell, maybe other more solid objects that maybe food. The lighter shade in the centre may be hole through which the jelly creature reaches out it’s long arms to catch it’s food. Maybe even to move, but not today. The bubbles within the shell expand and contract slowly, the edges of the creature appear to form a crimping from the inner crust. It looks like an amoeba in a flat cap, or what Dr Suess might have called, a Splat in a Hat.
Follow up research
Identifying this microorganism was relatively quick. On the cover Marjorie Hingley’s Microscopic Life in Sphagnum, there is an illustration that looks very similar. On page 15 there is a very simple line drawing which is denoted as Arcella (saucer shaped). It is a shelled amoeba, also known as case-baring amoebae or testate rhizopods. A species, not dissimilar to my specimen, is illustrated in colour Plate 4 as Arcella discoides.
It didn’t take me long to observe another Acella, this time one in action: moving and absorbing its food. However, these are not wild carnivores like Wyndam’s kraken, they are gentle giants herbivores like the zebra or even the rhinos of the savanna. They feed on passing algae, diatoms, fungi and bacteria.[1] We are still finding new species. In 2016 a new species was found in Brazil and named Arcella gandalfi, because it’s teste is a funnel shape like a wizards hat. [2]
Maybe I was right, a splat in a wizard’s hat!
[1]Meisterfeld, Ralf and Edward Mitchell. 2008. Arcella Ehrenberg 1832. Version 02 September 2008 (under construction). http://tolweb.org/Arcella/124482/2008.09.02 in The Tree of Life Web Project, http://tolweb.org/
Moss Safari 