Cetaceans

Baleen whales include the great whales or rorquals, a word that comes from the Norse for "grooved whale," owing to the conspicuous grooves or pleats on the throat and belly of these huge animals. There are seven rorquals, including the blue whale (Balaenoptera musculus), the largest creature that has ever lived. The largest blue whale ever recorded, according to the Guiness Book of World Records, was a female caught in 1926 off the Shetland Islands, measuring 109 ft (33.3 m) long. The blue whale belongs to the family Balaenopteridae, a group that migrates from summer feeding grounds in cold polar waters to breed in warmer waters in the fall and winter. Additional species are the fin whale (B. physalus), sei whale (B. borealis), Bryde's whale (B. edeni), minke whale (B. acutorostrata), humpback whale (Megaptera novaeangliae), and gray whale (Eschrictius robustus).

Rounding out the baleen whales are the Balaenidae, three genera that include the right whale (Balaena glacialis), the bowhead whale (B. mysticetus), and their elusive cousin, the pygmy right whale (Caperea marginata). Many cetologists recognize three subspecific forms of the right whale, and some argue that the southernmost of these deserves recognition as a separate species, the southern right whale (B. australis).

Although baleen whales are very large, they subsist on some of the smallest creatures: tiny oceanic plankton, or krill. Mysticetes are filter feeders, straining the water to collect their microscopic food, swallowing them in vast numbers; one mouthful of water may net its owner tens or hundreds of thousands of these tiny prey, which are trapped on the baleen as the seawater rushes back out. The baleen are rows of flexible, horny plates suspended from the upper jaw, each one fringed with a mat of hair-like projections to create an effective filtering device. Baleen was used for many years in ladies' corsets and other fashions, and thus was given the misleading name "whalebone." It is not bone at all, but rather the tough, flexible protein called keratin. As a group, baleen whales are larger and slower moving than toothed whales, perhaps in part because they do not need to pursue their prey.