Sea nymphs of the Mediterranean: the fifty granddaughters of Pontus the sea god and Gaea the earth mother. They have some relationships to the mermaids of other seas and oceans, and like them are extremely beautiful, but they do not have fishtails.
Some nereids, such as Galatea and Thetis, occupy important positions among the gods. Thetis is so beautiful that numerous gods sought to marry her, but she avoided acceptance until the great god Zeus insisted on her union with the King of Thessaly. Thetis thought that marriage to a mortal was so degrading that she evaded the king's courtship, by turning herself into such shapes as a flame, a wave, and a fish. But the king persisted, and made her the mother of the hero Achilles.
All the other nereids have remained virgins, and they spend most of their time gambolling through the waves with the dolphins and tritons who accompany the chariot of Poseidon, Lord of the Ocean.
Nereids, like the mermaids of other waters, are exceedingly vain. When they heard that Cassiopeia of Ethiopia had boasted of her daughter Andromeda, saying that she were more beautiful than the nereids, they were so insulted that they asked Poseidon to punish the mother and daughter.
Poseidon obliged by sending a monster to ravage Ethiopia, and would not recall it until Andromeda had been chained naked to a rock in the sea. Luckily the hero Perseus fell in love with the naked maiden, killed the monster, turned Andromeda's fiancÚ and his friends into stone by showing them the Gorgon's head, and married the young princess.
Avaricum | The Legend of King Arthur