After a bit more web-searching:
http://www.sciencedaily.com/releases/20 ... 094450.htmMind-blowing. They don't have mitochondria at all, but bacteria-like hydrogenosomes. That is such a major change that I have to wonder if it's a survival from far in the past, rather than a recent development.
Note that the link also leads to two (free) scientific articles on the subject. I'm reading 'em as I type.
EDIT: They also apparently have symbiotic microbes, which may well be Archaea instead of bacteria. That also would be strange and interesting.
I'm not yet clear on what they're respiring from the environment. They produce hydrogen, but from what? Their habitat is full of hydrogen sulfide, maybe that's it?