Well, to be precise a Vorticella. A microscopic creature which looks a bit like an upside down bell. The top, the mouth opening, is surrounded by cilia which rapidly wave up and down in turn. This helps to suck minute food particles towards the opening. On the video they are moving so fast that at first glance I thought the top was rotating. From the bottom of the Vorticella is a stalk which it can use to attach itself and also coil it like a spring to rapidly move out of the way of danger.
By photographing the slide scale at the same size as the video view and making the background transparent it was possible to add the scale on the video. I tried for ages to get the background transparent in Affinity Photo but the result was poor so ended up going to my old copy of Elements which did it in three quick operations. Magic Wand to surround the black markings, hit delete to make the background see through. Save as .png. Job done!
3 hours ago