Atlantica
Atlantica is the homeworld of Ariel, King Triton, Eric, Melody, Scuttle, Sebastian, Flounder, Tip, Dash, Grimsby, Ursula, Morgana, Undertow, Evil Manta, Saleen, Marina Del Ray, and Queen Athena. Almost completely underwater, Atlantica is a rocky world with immense holes on its surface. Beneath the surface is an entire world full of fish, merfolk, and other aquatic species that make up King Triton's underwater kingdom. The Heartless that appear in Atlantica are unique to it, such as Sea Neons, which resemble jellyfish. The mermaids dominated the seas while the humans there control the lands. Mermaids formerly tried to avoid contact with the humans for several reasons such as the consumption of sea creatures until the events of The Little Mermaid where Ariel and Eric's relationship brings peace to both races and defeats the evil Ursula. In The Little Mermaid 2: Return to the Sea, when mermaids and humans continued to coexist in harmony (And it's assumed the humans gone vegetarian to maintain the peace with the mermaids), Ariel and Eric give birth to their aquatically-addictive daughter, Melody, who was banned from the sea due to Morgana for 12 years until she managed to defeat the Sea Witch. Since then, Atlantica was in peace once again.