A sea-nymph, beloved by Polypheme, but herself in love with Acis. Acis was crushed under a huge rock by the jealous giant, and Galatea threw herself into the sea, where she joined her sister nymphs. Carlo Maratti (1625-1713) depicted Galatea in the sea and Polypheme sitting on a rock. Handel has an opera entitled Acis and Galatea.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894