Blue whale is the largest creature of the sea. In fact, it is the largest creature known to man. Contrary to what most people think, even though Blue whales live in the sea, they are mammals. They breathe air, have their babies born alive and can live anywhere from 30 to 70 years. Blue whale is a baleen whale, and instead of having teeth. Blue whales have around 300-400 baleen plates in their mouths. Whales are separated into two groups, the baleen and the toothed whales. The blue whale is the largest baleen whale and the largest animal that ever lived on earth, including the largest dinosaurs. Baleen is rows of coarse, bristle-like fibers used to strain plankton from the water. Baleen is made of keratin, the same material as our fingernails.