The largest creature ever known to have existed is the Blue Whale. Its dimensions are impressive. But, perhaps even more notable, is the fact that this gigantic creature enjoys a diet of the smallest prey of any other cetacean and some of the smallest creatures eaten habitually by any carnivore. This prey is known as plankton or krill, and is a miniscule crustacean that is usually found in groups (or swarms) of thousands of individuals.
Unlike toothed whales, baleen whales feed by means of a baleen plate (sometimes known as whalebone). This plate is made up of bristles made of long hairs, each of which is covered by a thin layer of horn until the tip, which is exposed and separated from the other hairs to form a fringe. These plates are supported by connective tissue that is attached to each side of the upper jaw.
The basal plates each form a separate baleen plate and are formed by several rows of papillae that have fused. The epidermal layer that covers the papillae, basal plates and spaces between the plates produces the horny matter that makes up the baleen plates.
Blue Whale from the air.
The size and colour of the baleen of various whales depends very much on their species. In order to allow the whale to close its mouth comfortably, the baleen plates fold so that they lie on either side of the tongue. When the mouth is opened, they spring back into form and extend from the top jaw to the bottom, held in place by the bottom lip, which prevents them from springing out of the mouth completely. The top of the mouth is arched to accommodate the baleen.
Baleen whales feed by swimming, open-mouthed, through large swarms of plankton. Sizeable gulps of water are pulled through the hairy baleen; trapping the tiny krill in the bristles and then forcing the water back out. For this to occur, the whale uses its tongue to either increase the capacity of the mouth or to force the food down the animal’s throat. Of course, the swarms of plankton may occasionally have other fauna and flora within them, which the whale would then swallow with the rest of its mouthful of krill. However, plankton generally travels with others of its species, limiting the other plants and animals from infiltrating their swarms.
Baleen whales move slower than toothed whales, since they do not need to pursue fast-moving prey that is trying to escape. They are also, generally, larger than toothed species. This is remarkable, since its prey is so much smaller than the squid, fish and small marine mammals on which other toothed cetaceans dine. Because they are larger and slower moving, they require thicker blubber to provide warmth and energy.