There are about 80 species of cetaceans, a group that includes whales, dolphins and porpoises. Cetaceans play an important role in the life of the ocean, serving as flagships for the health and well-being of the whole marine ecosystem.

Cetaceans are air-breathing, warm-blooded mammals that bear live young and nurse them on milk. The study of fossils indicates that cetaceans evolved from four-legged, terrestrial ancestors that made their way back to the seas around 55 million years ago.

Cetaceans fall into two categories: baleen whales, or mysticetes, and toothed whales, or odontocetes.

Humpback Whale WWF-Canon / Cat Holloway

There are 13 species of baleen whales: blue, fin, sei, Bryde's, humpback, northern minke, southern minke, North Pacific right, North Atlantic right, southern right, pygmy right, bowhead, and gray. They range in size from the compact minke whale, whose average length is around 33 feet, to the gargantuan blue whale, which can reach lengths of over 100 feet and weigh as much as 32 elephants! Distinctive characteristics of the baleen whale include a symmetrical skull with no melon -- the apparatus used by odontocetes for echolocation -- and a pair of nasal cavities, or blowholes, instead of the odontocetes' single blowhole.

Toothed whales are a diverse group of more than 70 species, range in size from the approximately 5-foot-long harbor porpoise to the mammoth 60-foot sperm whale. Some other examples are the bottlenose dolphin, spinner dolphin, Indus River dolphin, orca (killer whale), pilot whale, beluga whale, narwhal, finless porpoise, and the rather large family of beaked whales.

Thirteen whale species are commonly referred to as the "great whales" or "large whales" – these include the 12 baleen whales listed above and sperm whales.

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