All whales, dolphins and porpoises belong to an order called cetaceans. Totaling approximately 78 species, cetaceans are divided into either of two groups: the mysticeti and the odontoceti, or baleen whales and toothed whales, respectively.
Baleen whales are so named because of their overlapping layers of baleen plates, which are composed of a fingernail-like substance called keratin. After the whale ingests a huge volume of seawater, they use the baleen as sieves for collecting microscopic organisms as the seawater is ejected from the whale's mouth. Baleen whales are the largest of all cetaceans, representing 11 distinct species across four families. These families include the right whales, pygmy right whales, gray whales and rorqual whales.
In addition to the presence of baleen, mysticeti whales can be differentiated from toothed whales by identifying the presence of two blowholes on top of the head. Toothed whales have only one blowhole.
Toothed whales are so named because they have teeth, as opposed to baleen. Depending on the species, toothed whales can have as many as 250 individual teeth. Toothed whales are more diverse than baleen whales, representing 67 distinct species. These species include such cetaceans as the killer whale, beluga whale and the bottlenose dolphin.