Microscopy Forum

Was it moving fast?  A (not-very-well-informed) guess: could this be Tetrahymena sp.?

By the way, does your microscope camera/software have provision for adding a scale?  If so, I think it would often help identification if you can add the scale bar to the image.  If not, and if you don't have a stage micrometer (on Ebay they go for $20 to $25), you can improvise by using a mm scale/ruler (take a photo with the 4x, then scale it up (e.g., at 40x its image will be 10 times longer; extreme accuracy is obviously not needed for this purpose).