I've been always amazed that fire has not invented by one branch of animals. It would have been great, you'll need a very tough stomach and a mother who breathes into you her fire when you are born. And of course, some sophisticated cooling mechanism would be required as well. However, after this, you can eat things, very few other animals can eat. Perhaps, if oil was closer to the surface, this would have been a valuable path for evolution.
To be able to handle an acidic solution seems less of a feat.