The Oilstone streak that had been blooming along the seafloor, spreading like a blight, broke open with a splintering crack. Oily fluids billowed out like black smoke into the water, but more importantly, Fornax's seawater poured back in. The monstrous beast within, near frantically trying to claw its way out, realized it was breathing water and at once redoubled its efforts.
Panic rose. Claws gripped at the edges of the Oilstone, held--and slipped away.
It took Manticore a moment to realize that he was... okay. He wasn't drowning, at least. He was... it was as though he were out of breath, weakening, but he could breathe. He struggled to steady himself, that fear riding the edges of his mind, and--blinking glowing eyes against the darkness--examined the ragged hole bleeding his chrysalis away.
Several minutes of more careful efforts freed him. Then he was out--in the water, ascending, his finned tail propelling him upward, his wings a drag downward so that he had to wrap them to his flanks. Light danced down into the darkness from above, rays casting like searchlights, and he made for that: leaving his place of birth behind, below, in favor of the sun and sky.
What he emerged into was nothing of the sort--the vast open cave of Fornax, its "sun" and "sky" mere pinpricks of light high in a cave roof. Manticore didn't know any better; he came up to the surface and lay floating there, wheezing as his gills expelled the last of the water in streams along his neck. He bobbed there like a duck, looking around, before starting a clumsy doggy-paddle for the only thing that he could see: the pebbly shore.
@Spinnaker @Mossie