Oannes

Greek rendering of the Sumero-Babylonian god Ea,
because of his connection with waters sometimes depicted as half man,
half fish. In daytime he lived with men to instruct them in the arts
and sciences, but at night he returned to the depths of the Persian
Gulf.

Oceanids

Oceanids, from Greek mythology, were the nymphs of the great ocean, the daughters of Oceanus and Tethys. There were well over 4,000 of these oceanids. They were sometimes shy, but at other times they were passionate lovers. Most of the time nymphs were kind to mortals, but they sometimes punished people who mistreated them. In the forest, nymphs were epresented with fauns and satyrs. You could sometimes find oceanids playing around the keels of ships. Nymphs lived for a long time, but they were usually not considered immortal.