as for the initial topic: We indeed don't know what the ancients called the planet before the terminus (it's entirely possible though that they did literally just call it the star, after all Earth isn't that imaginative of a name either). Zodiark was created as "the will of the star" itself, so he and the planet became synonymous. And later our mommy crystal took over that role after banishing Zodiark.
So yes, Hydaelin is the planet.