Ancient Corinthian vase depicting Perseus, Andromeda and Ketos. Note the usage of Epsilon instead of Eta in ΚΕΤΟΣ, the employment of the letter San instead of Sigma in ΠΕΡΣΕΥΣ and ΚΕΤΟΣ.
In Greek mythology, Ceto or Keto (Greek: Κῆτος (neut.), English translation: "sea monster") was a hideous aquatic monster, a daughter of Gaia and Pontus. The asteroid(65489) Ceto was named after her, and its satellite (65489) Ceto I Phorcys after her husband. She was the personification of the dangers of the sea, unknown terrors and bizarre creatures. Eventually, the word "ceto" became simple shorthand for any sea monster. The term cetacean represents a case in point. Her husband was Phorcys and they had many children, collectively known as the Phorcydes or Phorcydides. In Greek art, Ceto was drawn as a serpentine fish. Ceto also gave name to the constellationCetus.
In Jonah 2:1 (1:17 in English translation), the Hebrew text reads dag gadol (דג גדול), which literally means "great fish." The Septuagint translates this phrase into Greek as ketos megas (κητος μεγας). The term ketos alone means "huge fish," and in Greek mythology the term was closely associated with sea monsters. Jerome later translated this phrase as piscis granda in his Latin Vulgate. However, he translated ketos as cetus in Matthew 12:40. Another figure named Ceto is an Oceanid, daughter of Oceanus and Tethys.