Whales and dolphins belong to a group of animals called cetaceans. They can be divided into two families:
Toothed whales have teeth, though these may not always be obvious. These whales use sound waves in a method called echolocation to navigate and hunt for fish and squid. New Zealand examples include sperm whales, pilot whales and dolphins.
Baleen whales have plates of baleen suspended from the roof of their mouths, through which enormous quantities of krill are sucked from the water. These whales are generally larger than toothed whales and include the largest whale of all, the blue whale. New Zealand examples include humpback and Southern right whales.
See information about common whale species below. Killer whale/orca are actually the largest member of the dolphin family.