And isn't it the case that Jane Webb and Jane Edwards were the same person?
Hmm. IMDb lists them separately, but Wikipedia says that Edwards was Webb's married name and that she played both characters. Not sure why Filmation would've billed her twice on the same show, though, given that it was pretty routine for most of their cast members to play multiple roles.
Ah, except I found the credits on YouTube
, and, unusually for an animated show, it credits the entire cast in the opening titles, in the style of the original show. (Following the TAS precedent, I guess, but that was only three actors/characters while this is seven.) So I guess the fiction of Webb and Edwards being different people was employed to justify crediting Ginger and Mary Ann separately. Whereas on the Gilligan's Planet credits
(holy cow), they swapped the positions of Ginger and the Professor so that both Dawn Wells characters could be billed consecutively.
Oh, now I'm going to have that theme music running through my head all day...