Let's not pile upon Yarn so much. His was a fair question.
Yarn, there were members a while back who proposed a separate sub-forum focused upon the 1973 Filmation animated series, but board admins speculated the traffic for such a section would be minimal at best. And as Forbin pointed out, the timeline presented in the animated series appeared to be part of the "five year mission" (since Shatner repeats the opening credit monologue word for word), so it was decided to let any threads about M'Ress, Arex and any other elements unique to the early 70s cartoon series reside in this section.
But again, I can understand your puzzlement about a "furry" appearing in Trek. M'Ress appeared in only 5, maybe 6 of the 22 episodes produced and rather like Uhura in the original series, she wasn't given much to do other than operating the switchboard. Her biggest moment was in "Mudd's Passion" when she was affected by the con artist's "love crystals" and temporarily fell for Scotty. So don't feel bad; even if you've seen the animated episodes, it's easy to have missed her.
Though in 6, she's not in the M'Rest of the episodes. Someone was aking above who would play her if not Majel, in TMP. We were speculating on guest actors if Phase II had gone ahead, in another thread. So let me propose here one name: