What about Isis and Sylvia? I think they were the same animal actor, in cat form.
So did the cat get paid more than the actress since the cat had "speaking" lines?
I jest...just one of those days
(But I did like when Isis the cat was on Seven's back meowing at him while he was trying to disarm the rocket
No kidding, I read that the little dog that played Toto in Wizard of Oz got paid more than the Munchkins, I think with that much screen time on Robert Lansing's back meowing must have been compensated. I'm sure the cat would have made more than the woman that sat there speechless and nearly motionless for a second. And animal actors are frequently billed, so I'm a little suprised the cat wasn't in either episode.
Regarding small speaking parts that aren't billed, an actor can ask not to be billed, especially if that actor doesn't want that on their resume. And Star Trek might have been the kind of show someone didn't want to admit working on, at the time.