[HoneyBadger]

I'm not really thinking the "original" Abyssian being a direct evolutionary forerunner so much as a chaotic primal magma "spring" from which the Abyssian Race "flows", kindof vaguely in the same vein as the Aboleth Polypal Mother, but male instead of female. While originally an Abyssian like the rest, the Prime Abyssian instead chose to remain in the Smouldercone and become it's heart. Now that I think about it some more, the Prime Abyssian could be the "father" of the Magma Children, and might produce them or something similar. This wouldn't be Rhuax, though, the Prime Abyssian would be Abyssian only with the idea that it/he (emphasis on "it" though) lives inside the Smouldercone, functioning as the classic "Volcano God". The Prime Abyssian might also backgroundwise explain why Abyssians can blood-sacrifice, since they'd toss their virgin captives into the Smouldercone to feed the Prime.