I've had a jar of pond water on the window sill for about three months now. A couple of times a week I give it a blast with an airstone and occassionally do a survey to see what is going on. At this stage it supports mostly one-celled algae and fast-moving protists. I rarely use objectives above 20x to survey pond water, but the other day I was checking out something with a 40x and found a small amoeba. I went back to the 20x and found there were dozens of these amoebae in a single drop.
They appear to be Amoeba guttula. They extend one or two short stubby pseudopodia but their particles don't flow into the pseudopodia -- they pretty much stay in a cluster in the main body.
Nikon MPlan 40x 0.65 210/0 with UGF illumination.
Images made through a microscope. All subject types.