drawings by William Ells with additional notes by David Walker
Introduction
Garden ponds are becoming more and more popular and they can
provide many fascinating subjects for the amateur microscopist.
They are a 'world within a world' and contain a surprising
variety of single-celled and multi-celled organisms.
One of the best ways to learn about the structure of an organism is to draw it. The sketches below are of microscopic organisms that may be found in a pond, and have been drawn by Bill Ells, Maidstone, UK.
Multi-cellular or uni-cellular?
There are twelve organisms shown in the accompanying diagrams,
four are multi-cellular and the remainder uni-cellular. The name
in italics below is the genus to which each organism belongs. The
text in quotes are remarks by the illustrator, Bill Ells.
One of the fascinations of studying pond-life is the incredible variety of shapes, sizes and behaviour of these microscopic organisms. Here are a few you might find.
Rotifers
Rotifers are muti-cellular organisms and have discrete organs
such as a heart and eye.
A: Squatinella. This rotifer has a conspicuous transparent
shield over the head, and the eyes have lenses.
B: Colurella. This is a sessile rotifer i.e. it attaches
itself to an object by means of it's foot.
Colurella features in a Micscape article where a
female's egg is attacked by protozoa. See
The Good, the Bad and the Ugly .
C: Collotheca. "The cilia of these species do not
wave about they are withdrawn into the body of the rotifer,
taking food in. In the withdrawn position they look like shaving
brushes."
D: Philodina. "The cilia of these species really look
like wheels". This is P. roseola a species of rotifer
often found in bird-baths. See The 'wheel-animal in a
bird-bath' .
Protozoa
E: Coleps These are the armoured tanks of the protozoa
world and also feature in the The Good,
the Bad and the Ugly . Bill remarks "when I first had a
microscope in 1976 my wife and I spent several hours watching
these dividing, the 'barrel' comes apart in the middle but the
two halves remain joined by two transparent hemispheres, one on
each half, they eventually break apart and the hemisphere grows
to complete the new Coleps".
J: Amoeba (Vexillifera?) This amoeba has spiny
pseudopodia.
Algae (Microscopic plants)
The first two algae below are desmids which are a fascinating
group.
Typically each cell is divided symmetrically into semicells which
are mirror images of each other.
H: Closterium. "These were abundant in the sample, 41
cells being found in two drops of water, one seen dividing."
I: Cosmarium. "A variable species".
F: Scenedesmus. Two different species are shown.
G: Gonium. Consists of colonies of cells.
K: Gomphonema growing on the branched filamentous alga Cladophora.
Gomphonema is a diatom, another fascinating group of algae
which have silica cell walls, the two halves of which fit
together like the old pill boxes. Resolving the fine details on
the shells of many species is a popular challenge for amateur
microscopists.
Comments to Bill Ells welcomed.
Further Reading
1) A Beginners Guide to the Collection, Isolation, Cultivation
and Identification of Freshwater Protozoa by B J Finlay, A
Rogerson and A J Cowling. Published by the Freshwater Biological
Association, The Ferry House, Ambleside, UK, 1988. (78 pages)
ISBN 1 871105 03 X.
2) A Beginners Guide to Freshwater Algae by H Belcher and E Swale. Published by the Institute of Freshwater Ecology, Natural Environment Research Council, Cambridge 1978. (47 pages) ISBN 0 11 881393 5.
Acknowledgements.
The Micscape editor's thank Bill Ells for contributing the
drawings and additional commentary which first appeared in a
Newsletter of the Kent and Sussex Microscopy Group, Spring 1993.
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