Ceto is one of the first founding Titans. She and Phorcys were the parents of Stheno & Euryale, along with their other daughter, Medusa. Her other children are the Graeae. Ceto shows no interest in Medusa whatsoever, Medusa was mortal, and Ceto, Phorcys, the Gorgon sisters and the Graeae were all immortals, so they were ashamed that they had mortals in their family. Ceto is the mother of all sea monsters in Greek mythology.
Ceto is often driven away from her real emotions, because she seems to show no interest at her daughters or her husband. She was only shocked when Medusa turned into a gorgon, but her sisters were already turned into ones, so she wasn't surprised.
Some of the founding Titans were the involvement of Cronus' genitals getting thrown into the sea. The other founding Titans that are closely related to Ceto and Phorcys is Thaumas and another sea Titan, Eurybia.