This cross section of the mouth of a humpback whale shows the baleen plates attached to the roof of its mouth. When the whale opens its mouth it takes in seawater and krill — shrimplike marine crustaceans. It then expels the water through its baleen plates, trapping the krill, which are then swallowed. Baleen grows throughout the whale's life, and is continually worn away at the end of the plates. It is is made of keratin, which is the same substance that human fingernails and hair are made from. Baleen whale species include the humpback whale, right whale, fin whale, and blue whale.