Mysticetes (Greek, mystax = moustache) are whales that do not have teeth. Instead, their mouth is lined with a series of baleen plates that resemble combs. This apparatus helps to strain plankton (krill) which is their main source of food. Some baleen whales are able to expand folds of skin in the throat to accomadate great quantities of water. The water is strained out through the baleen and the krill is trapped and ingested. They have two blowholes at the top of their head, a symmetrical skull and no melon. Mysticeti usually has a larger body size than Odonticeti.

It is interesting to note that fossil Mysticeti have teeth, demonstrating their derivation from Archaeoceti which had teeth.