Homo mermanus - Young Justice: Phantoms

The descendants of both Vandar Adg (the first Homo meta) and Arion (the first Homo magi), Homo mermanus were born during the horrific cataclysm that destroyed their home, the continent of Atlantis. 

Undergoing extreme psychological and physical distress, the devastated remnants of the Homo magi developed the ability to breathe underwater when their latent meta-genes were forcibly activated, leading to their eventual evolution into the modern-day Atlanteans. 

Homo mermanus continued to expand across the seven seas, till at last the new kingdom of Atlantis controlled 3/4ths of the Earth.