What is the underground water biome in calamity?

Terraria Calamity Mage

So the Sulphurous Sea got reworked

Check out my calamity mod snow biome base. : r/Terraria

Playing on calamity mod. I need to know this biome and what it is please answer fast : r/Terraria

What is the underground water biome in calamity?

NEW Sunken Sea Biome! Terraria Calamity Mod Let's Play #7

I can't find my Sunken Sea biome, any help would be greatly appreciated. I wonder if it didn't spawn because my one underground desert goes all the way to hell. : r/CalamityMod

So Is this normal for this biome? (Calamity mod) : r/Terraria

Terraria Calamity Mod. ENG/ESP

Abyss - Official Calamity Mod Wiki