The opening sentence of Wikipedia's article on the man seems fairly encompassing:
Terence Kemp McKenna (November 16, 1946 – April 3, 2000) was a writer, public speaker, philosopher, psychonaut, ethnobotanist, art historian, and self-described anarchist, anti-materialist, environmentalist, feminist, platonist and skeptic.
However, it doesn't say anything about cephalopods, and that is a serious oversight. Apparently McKenna believed that they were the totemic images. Really. See, I got this quote off the SF Chronicle's blog:*
I believe that the totemic image for the future is the octopus. This is because the squids and octopi have perfected a form of communication that is both psychedelic and telepathic; a model for the human communications of the future.
Wow. That's . . . something. I don't think we've found any evidence of telepathy in cephalopod communications. And technically,
A psychedelic experience is characterized by the perception of aspects of one's mind previously unknown, or by the creative exuberance of the mind liberated from its ostensibly ordinary fetters.
which is kind of the opposite of cephalopod communication, in which individuals can continuously percieve known, ordinary signals from each other.

But, if you're going for a more casual definition of psychedelic, it's hard to imagine a more fitting example than Wunderpus photogenicus:

I'm just not exactly clear how to take this as a model for human communication.

* Man, it would have been really cool to make it to that workshop.