Ketos

A kētos (κῆτος, plural kētē or kētea, κήτη or κήτεα)—Latinized as cetus (pl. cetea)—denotes a large fish, a whale, a shark, or a sea monster. The sea monsters slain by Perseus and Herakles were each referred to as a ketos by ancient sources. A ketos is commonly a fishlike or serpentine aquatic creature with a long muzzle. Alternate depictions may include long ears, horns, and legs instead of fins.

One is often depicted fighting Perseus or as the mount of a Nereid.

When Queen Kassiopeia boasted that her daughter Andromeda was more beautiful than the nereids, this invoked the wrath of Poseidon who sent the sea monster Ketos to attack Æthiopia. Upon consulting a wise oracle, King Kepheus and Queen Kassiopeia were told to sacrifice Andromeda to Ketos. So they had Andromeda chained to a rock near the ocean so that he could devour her. Perseus found Andromeda chained to the rock and learned of her abondonment and impending doom. When Ketos emerged from the ocean to devour Andromeda, Perseus managed to slayed him. In one version, Perseus drove his sword into Ketos' back, while in another version, Perseus used Medusa's head to turn Ketos to stone.

Legacy
The term cetacean (meaning 'whale') originates from cetus. In Greek art, ketea were depicted as serpentine fish. The name of the mythological figure Keto is also derived from ketea, as well as the constellation Cetus.

Cetus is commonly used as a ship's name or figurehead denoting either a ship unafraid of the sea or a ruthless pirate ship to be feared. Cetus (and its translations) are also viewed as misfortune or bad omen by sailors. Superstitious sailors believed in a cetus as the bringer of a great storm or misfortune on the ship. They associated it with lost cargo, the presence of pirates, or being swept off course, and avoided any talk of it aboard ship.

Meta
Some scholars theorize that images of the ketos in Central Asia influenced depictions of the Chinese dragon and Indian makara. They suggest that after contact with Silk Road images of the ketos, the Chinese dragon appeared more reptilian and shifted head shape.