Generally speaking, although scientifically incorrect, a cetacean is considered a whale if it is over four metres long, and any other cetaceans measuring less than 4 metres belong to the dolphin family. The other Cetaceans comprises two groups:
- Toothed cetaceans (odontoceti)
- Baleen cetaceans or whales (mysticeti).
The rest group, toothed cetaceans, include dolphins, beaked whales and sperm whales, all of which use their teeth to capture prey, which is then swallowed whole. The mysticeti order of cetaceans, associated with large whales, have plates hanging from the upper jaw, allowing them to lter sea water and capture food such as krill or small fish.