Not even Namco knows
I'm just going to say he is a new species of some sort.
Seems like there are a few similar to his kind in phantomile though.
You could think of phantomile as realm where the beings are embodiments of their respective consciousnesses or soul maybe both.
Because wth is a Ghadius or a Moo even Nahatomb seems like an unidentifiable thing if not some distorted being it's self

poor thing.
Lunatea seems to follow a similar strangeness I mean look at popka's eyes what creature needs that kind of pupil in their eyes?
The king of sorrow seems to be an embodiment of his respective essence or maybe a consciousness that attached to it.
I can't even pin down what Phantomile and Luntea are supposed to be they are realms supported off dreams but whos it seems like many dreams exist for some reason but are relatively unknown?
The world phantom in Phantomile might be a hint to that but with no certainty.
There is all my theorizing for now.
For me Klonoa is a being born from a consciousnesses or soul of some origin the appearance is based off what I said earlier.
Edit: Klonoa says manya or magya when he gets hurt. on the wii version it almost sounds like hanya to me but I prefer phatomillian speak Klonoa over other languages.