Freshwater organism under microscope - Part 4

Any idea what this is? I believe I used a 10x objective.
I sampled a drop of water from an aquarium that hasn't had any fish in it for well over a year. 2 years? I don't remember. The last I remember seeing in it were some planaria...
I need to learn how to add a scale bar in Swift Imaging, but I have a feeling this will be a very recognizable creature to any halfway experienced hobbyist.
Whatever this is, I believe it was dying due to the weight of the cover glass on the slide.