My brother has a salt tank with several tiny octopi and he says they are very intelligent. He gives them toys and puzzles to keep themselves occupied.
The book "Creatures of the Abyss" is very cool. Lots of fascinating beasties.
I sent the link to my friend sculptor Ver Mar http://www.vermarart.com/sculptures_frames.htm and she is incorporating a lot of weird real animals into her fantastical pieces.