the term ‘macrofauna’ doesn’t get your attention, nothing will.

It sure got my attention. Examples of macrofauna would include giant squid, sharks, and whales. The latter would be impossible to find swimming the Europan ocean (whales evolved from land animals) but animals the size of these creatures would have no lack of oxygen or energy to live on this moon. And depending on the mineral content, possibly without environmental suits.
Another interesting point: there might be far more extra-terrestrial environments hospitable for dolphins and whales than for humans.