Whales belong to Chordata, Vertebrate, Mammalia and Euthera, including about 98 viviparous mammals living in oceans and rivers. There are more than 30 species in China waters. All cetaceans live in the sea except a few that live in fresh water.
The definition of whale itself is vague. Cetaceans can include all cetaceans, as well as cetaceans of specific families. The cetaceans also include all dolphins.
Cetaceans are mainly divided into two suborders: baleen whales and toothed whales. There are fewer species of baleen whales, but they are huge. The smallest known species is more than 6 meters long. The blue whale, the largest animal in the world, also belongs to baleen whales.
However, the shape of toothed whales is quite different, the smallest species is only about 30 cm long, and the largest sperm whale is more than 20 meters long.