When you look down the microscope, you often meet bacteria. They are unicellular prokaryotes. Usually, they are much smaller than protists. They are often hardly visible down the light microscope. Some of them are immobile, others move all the time.
Bacteria often feed on dead protists.
Flexibacter This is a very mobile bacterium, probably a Flexibacter. It is shaped like a contorted wire. They are also called Cyanophyceae. They were probably the first organisms on Earth able to produce nutrients to feed themselves. They originated over 3.8 billion years ago.