I'm a bit reluctant to be that guy, but... E. coli is not an animal... There are some really small animals, though: https://en.wikipedia.org/wiki/Rotifer http

I'm a bit reluctant to be that guy, but... E. coli is not an animal... There are some really small animals, though: https://en.wikipedia.org/wiki/Rotifer https://en.wikipedia.org/wiki/Rotifer https://en.wikipedia.org/wiki/Water_bear https://en.wikipedia.org/wiki/Water_bear