Octopus

The First Doctor frees John from the grasp of an octopus by tickling it. (TVC: Shark Bait)

Octopuses were a species native to Earth and at least one other planet. John was once grabbed by an octopus which restrained him with its tentacles. He was freed by the First Doctor when he tickled it with a feather. (TVC: Shark Bait)

Professor Zaroff had a pet octopus. (DW: The Underwater Menace)