Ok I know I said it'd be "funny" if they were bojacks but it honestly makes perfect sense, if adult nymphs look like barely-anthropomorphized bipedal squids like the Caretaker. Unless there's something funnier and better I can't think of, they pretty much have to be walking horses.

Meemaw... might actually be a different thing??? Like a primordial pre-nymph if she remembers Rose, the same kind of thing as that potted horrorterror that Terezi kicked (if she isn't literally that one, which I think is Certifiably Plausible).