Bhagavata Purana 5.24.29-31: Beneath Mahatala is the planetary system known as Rasatal, which is the abode of the demoniac sons of Diti and Danu. They are called Panis. They are all enemies of the demigods, and they reside in holes like snakes. From birth they are extremely powerful and cruel, and although they are proud of their strength, they are always defeated by the Sudarshana chakra of the Supreme Personality of Godhead, who rules all the planetary systems.
Beneath Rasatal is another planetary system, known as Patala or Nagaloka, where there are many demonic serpents, the masters of Nagaloka.