Dipnoi

Lungfish, also known as dipnoans, are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for their innovative respiratory system, including the ability to breathe air, and derived structures within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Lungfish represent the closest living relatives of the tetrapods. The mouths of lungfish typically bear tooth plates, which are used to crush hard shelled organisms.