I'd settle for a dedicated episode or two to Caitians in general. We know very little about their race, Caitia, language, ships, technology, society etc
According to a friend who once found the "TAS Writers' Bible" in the donated research archive (ie. the special science fiction collection) at the Paley Library at Philadelphia's Temple University. (It's a non-circulating collection, but anyone with a legitimate excuse can get permission to browse through specific items.)
Essentially, it's a TOS bible with an extra page or two added - there was a little hand-drawn map showing the location of Cait in the Lynx constellation, and another section briefly describing Arex and M'Ress.
So when they were generating her character at Filmation, even though no details ever made it to screen, they had some scant ideas. Perhaps they originally thought it might generate a script featuring M'Ress at some point?
I know I often wondered how Bjo Trimble's firs pro edition of the "ST Concordance" included the "Cait" and "Lynx" factoids for M'Ress, but nothing for Arex
beyond physical description. The TAS bible resolves that.
Later, Lincoln Enterprises were selling the Arex and M'Ress "biography" sheets, and it's possible those were written by Alan Dean Foster, although no author is credited on them. Other details on M'Ress (parents, siblings, past career highlights) can be found in ADF's expanded scenes of "ST Logs" adaptations, but there are errors re Arex. He describes Arex as having three eyes
, in one sequence, and looking over a "feathered shoulder" in another.
My guess is that the chief animators at Filmation created the look of M'Ress and Arex to address show-runner DC Fontana's urging that they come up with visuals that could not have been done easily in live action in the 60s.
Well there is still the chance that that alien on the Kelvin bridge was a member of Arex's race.
No, the 2009 creators have said no. And he lacks the third arm and leg!