There are over 80 species of Cetaceans, or whales, which are divided into two groups, or suborders, based on how they eat. The two suborders of Cetaceans are Odontocetes and Mysticetes. Cetaceans that have teeth belong in a very diverse group called Odontocetes, which includes over 70 different species. Toothed whales typically have a single blowhole and use echolocation to find their food, which they have to chew up to eat. Some examples of Odontocetes are dolphins, sperm whales, belugas, and narwhals (That’s right! The big unicorn horn on narwhals is actually a TOOTH!).
Credit: Chicago Zoological Society, Sarasota Dolphin Research Program
So if this other group of whales called Mysticetes doesn’t have teeth, then what do they have? Baleen. Mysticetes, quite literally means, “mustache whales,” named after all the bristly, hairy baleen in their mouths. Baleen is an elaborate structure made of hundreds of plates hanging from the upper jaw, while the inner surface makes a dense mat of hair acting as a strainer. This suborder includes over 10 species like the Humpback whale, Sei whale, and Blue whale (which happens to be the biggest animal that has ever lived! Even bigger than the Titanosaur!). Mysticetes have two blowholes, instead of one, and typically do not use echolocation to hunt. They eat by sucking in huge volumes of water (with prey in it), then spitting the water back out through their baleen, which traps the food on its inner surface.
For more information on Whales and their baleen visit https://www.redorbit.com/news/science/1112803585/baleen-whale-teeth-entangle-prey-031413/