Related: What's the biggest obligate anaerobic organism discovered till now?
I had always assumed that the Riftia tube worms were obligately anaerobic since they lived next to anoxic volcanic vents, but a quick literature search showed it to be a facultative anaerobe, being able to survive at least 60 hours without oxygen.
If "facultative anaerobe" is defined as being able to survive at least 24 hours in the absence of molecular oxygen in an otherwise normal environment, are there any metazoal organisms larger than Riftia (which are up to 1.5m long)?