Octopuses were a species of cephalopods (TV: Terror of the Autons) 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. (COMIC: Shark Bait)
Professor Zaroff had a pet octopus. (TV: The Underwater Menace)
There were methane-breathing octopuses on Neptune in the 32nd century. (PROSE: The Eye of the Tyger)