The people of the sea had a name for the vast ocean above the sky. They told their young stories of the sparkling schools of burning sea creatures that hid themselves behind the vast blue fin and blazing yellow eye of the mother whale that lit the arid ocean and warmed the waters of the sea. Cautionary tales were told to keep curious children away from the barrier between the sea and the arid ocean above. Those folk were strange creatures, breathing air instead of water and moving with thick legs instead of a single sleek tail as they did.
When merfolk breached the waves and experienced the dryness of the air, the strange weightlessness of the arid ocean and its lack of comforting pressure, could cause madness. Some folk would leave the sea altogether, living on rocks and eating rotting fish and seaweed, luring sailors and other hapless arid folk towards them and towards doom.