When you scrutinize a drop of water from a ditch or a hay infusion, there's a good chance you'll see amoebae. But you will really have to scrutinize indeed, because they are transparent, and with little contrast. The testate amoebae however, like this Arcella species, have little houses that make them rather conspicuous. In the case of Arcella, the housing is dome or helmet shaped, the diameter of this specimen is about a tenth of a millimeter. Because the opening is on the the underside, the amoeba mostly crawls over the slide, so we see the top of the house, like a small brown button. All pictures on this page are of the same specimen, possibly Arcella vulgaris.
On the picture above left a dark spot is visible under the scale, this may be an airbubble, on the picture on the right it's not there. And a hair like projection can be seen, this may be a 'foot' of the amoeba, a pseudopium. On both pictures the fields of the scale are well visible.
The small depth of field makes it necessary to lower the focus in order to see the pseudopodia. Like on the picture below: the scale is out of focus, but the projections are now visible: 'on 9 o'clock' a few thin ones, 'on 11 o'clock a broader flap. On the insert, the scale is pictured unsharp, but it gives a good impression of the form.