There are lots of anaerobic microorganisms .. It's generally believed that in the first half of earth's history, there wasn't much oxygen around and so early life was not oxygen dependent. Then there's a hypothesis that cyanobacteria, bacterias that are capable of (oxygenic) photosynthesis are "responsible" for first adding over time large amounts of oxygen to our atmosphere as it is a byproduct of photosynthesis.
edit :
As for that thing being a bacteria. Well, aside from other logical problems, bacterias are unicellular and generally very small. Much smaller than eukaryotic ("animal") cells. I guess that one would be a bit big for a cell
