Life in a Drop of Water

by Mike Morgan

How often have we seen, in books aimed at the amateur microscopist, that one drop of sediment and water from the pond, would yield a wealth of organisms to view and wonder at?

I tried this, observing over a period of one hour, 25 microlitres of sediment/pond water.

Indeed there were a wealth of organisms to wonder at. I decided to split these observations into different articles, covering the types seen. The first will show the types of Rotifer observed and I will follow this with articles showing the protozoa and algae / desmids.

Three types of rotifer were seen. The most abundant was Brachionus sp. and I was able to see the rotifer both with and without her carrying her eggs (image above and left respectively).

Next to appear was Anuraeopsis. There is only one British and Irish species of this rotifer, i.e. Anuraeopsis fissa. The asexual eggs are very distinctive in being tear-drop shaped and are carried attached to an anal appendage or egg carrier.

The third rotifer observed was Rotaria neptunia. The telescopic nature of the rotifer's movement was clearly seen, as were the 3 toes and 2 spurs on the foot.

The more observant may notice a few other organisms, captured alongside the rotifers. The ubiquitous Paramecium, for one! My next two articles will cover the various protozoa and algae seen in what, for me, was a very exciting hour's viewing of that "drop of water".

Further reading: A Key to British Freshwater Planktonic Rotifera by Rosalind M Pontin.
Freshwater Biological Association.

See a video clip showing the birth of a live rotifer of the genus Rotaria.


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