Bdelloid rotifer, an aquatic microorganism. "These little guys are pretty common in fresh water systems (and activated sludge plants, where I tend to see them). The little chainsaws are not actually rotating, they are extensions with many small vibrating cilia on them that just look a bit like rotating blades. The cilia create water movement into their mouths, which gets free free floating bacteria in there to eat them." (/u/Skudedarude) Also, they reproduce by parthogenesis lol