The Cetus is a large organism that lives in the vacuum of space. It is very large, and is at least 15 times larger than the Andromeda Ascendant. The crew encountered it in the episode Belly of the Beast.
It eats any type of matter (except antimatter), and has a very slow metabolism, only needing to eat every 6,720 years. When Andromeda scanned it, it found no central nervous system or brain, but patches of spread out neural fibre that control it. It has 5 large, petal shaped jaws that it uses to consume its food. The Cetus was killed by the ejection of Andromeda's Slipstream core. Its length is approx. 20-25 kilometers (~20 miles) (with closed petals). Without closed petals it is approx. 12-14 miles long.
- "Cetus" is Latin for "whale". This is reflected also in Harper saying "Call me Ishmael", the opening words of Melville's "The Whale, or Moby Dick".
- The whale image further ties into the title, with its Biblical connotations of the tale of Jonah.