Baleen whales are sometimes called "mustached whales." The name refers to the series of baleen plates in gums along each side of the whale 's upper jaw. They are triangular and arranged like teeth in a comb. The inner edge is frayed, and the fringes form a dense mat inside the mouth. Baleen is made mostly of keratin, a substance found in our fingernails and hair. Baleen whales, some of which are the largest animals to have ever lived on earth, eat some of the smallest, most abundant life in the oceans: plankton. Some baleen whales also eat small schooling fishes, and a variety of crustaceans such as krill, copepods, and amphipods. Baleen whales use baleen to strain food from the water. Some feed by swimming with their mouths wide open. Others