In Greek mythology, Thalassa (Greek: Θαλασσα, "sea"), also spelled as Thalasse (Greek: Θαλασση) or Thalatta (Greek: Θαλαττη), was the personified goddess of the sea, namely the Mediterranean. In the preface to Fabulae, Gaius Julius Hyginus describes her as the daughter of Aether and Hemera, as the consort of Pontus, and the mother of the fish. The Greek historian Diodorus Siculus describes Halia as the daughter of Thalassa. Pontus and Thalassa were the rulers of the sea before Oceanus and Tethys, who were eventually replaced by Poseidon and Amphitrite.

In art, Thalassa has been depicted as a woman clothed in seaweed and being submerged in the sea. She has crab claws coming out of her head like horns and is holding an oar and a dolphin.

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