There are 79 species within this order The terms "dolphin" and "whale" are applied to various cetaceans depending on body size, but there is no scientific discontinuity between the species of Cetacea.
海豚和鯨魚同屬鯨目，其下共有約七十九種，「海豚」或「鯨魚」是依體型的大小來稱呼，不具科學意義。