The Daedra changed themselves, and so consequencely they are no longer in their oringinal state. What they didn't do was give an entire part of themselves to create something, like the Aedra did. The spirits who did not become Aedric or Daedric, did not change themselves, or give parts of themselves to create/change anything, and remained as they were.
....What?????
Dude, this is how it goes: sans the "I'm-Anuic-but-Daedric" BS, all the Daedra are are the et'Ada who didn't give pieces of themselves to creation; in consideration to their spheres, they technically couldn't. The "spirits who did not become Aedric or Daedric" are either Y'ffre or the Star Orphans, one of which Mnemoli is.
Just ignore the Aedra-Daedra crap, at least in this aspect; the way I understand it, Dagon himself may not even have Padomaic origin, according to certain texts, the Alduggada (sp?) being one of these (if not the only one, if I understand right).
Dude, I think this has been overtalked so much I'M getting confused... I might even forget what the hell et'Ada are, if this continues lol...