There are two main families of whales, one with teeth (odontocetes) and the other with baleen (mysticetes). They are pretty easy to tell apart.
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Odontocetes have teeth for grabbing food and a single blowhole or nostril. The largest is the Sperm whale (50feet) but other members of this family include dolphins, pilot whales, narwhals, belugas, orcas etc. They eat fish, squid even other marine mammals.
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Mysticetes have baleen for filtering food and have two blowholes. The largest is the Blue whale (100 feet) others are finbacks, humpbacks, minkes, right whales, gray whales etc. They eat some small schooling fish but mostly huge dense concentrations of tiny krill, sand lance or copepods.