Stalking the Nightmare (1982) is a collection of miscellaneous short works by Harlan Ellison. One of the pieces, "The Hour That Stretches", is sort of a fictionalized transcript of a guest appearance by Ellison on the radio show Hour 25, hosted by Mike Hodel.
At Ellison's suggestion, callers to the show (including some of his writer peers) pitch ideas to him, which he then tries to develop into plot synopses for stories, improv style -- at least when he isn't insulting the callers or saving Humanity from mysterious, outer forces bent on our destruction.
After an idea about racing domesticated Arabian camels with NFL players as jockeys and someone suggesting he write "I'm Looking for Kadak" again, only with the Pope thrown in -- both of which he dispatched without synopsizing -- Ellison gets this call:
Hodel put on another caller. Mayer Alan Brenner.
"I know you," Ellison said.
"You sure do. And I've got a beauty for you."
"Be still my heart," Ellison said, sinking down on his spine.
"It's an excerpt from NORTHEAST TREE AND STREAM," Mayer said. "A short history of the famous Chesapeake Tree-Climbing Octopus..."
"Why me?" Ellison groaned. "Which God did I offend?"
"All of them," said Hodel.
Mayer went on, undaunted by sounds of pain coming over his radio.
"This retiring and rarely glimpsed creature lives in the many quiet estuaries of the Chesapeake system. Early each morning the octopus leaves the water and crawls up the trunk of a shoreside tree. It makes its way precariously onto a branch overhanging the water, where it waits for its prey to pass underneath." Silence ensued. Dead air hung heavily in the night.
Finally, Ellison said, "And that's it, right? That's the idea, right, Mayer?"
More silence. Then, in a very soft, very tired voice, Ellison said, "These blue-skinned Jewish aliens with wheels come down to Earth and kidnap the Pope so they can have a race on Arabian camels to establish whether Jews or Gentiles are worthiest to live in the universe, and the Pope gets all these NFL players to ride as his team, because they're all Polish or black and not a Jew in the lot, and they have this watercourse raceway and they race for the universe, and as they come under this tree in the Chesapeake system the octopus drops out of a tree and eats every last, fucking one of them, football players, Jewish aliens, the Pope, the camels, Brian Sipe and Terry Bradshaw and Walter Payton and you too Mayer!"
Ok, so it's not "Devilfish with a Glass Tentacle" or "A Boy and his Octopus", but it's still a Harlan Ellison story about a tree octopus. Now if I could just track down that issue of Northeast Tree and Stream that Brenner found...