An article that illustrates why the octopus would make a great model for an intelligent nonhumanoid alien:The Mind of the Octopus
Octopuses in captivity appear to recognize individual human beings. They are good at solving puzzles, such as getting into closed containers, and learn quickly. They perform playful activities and show evidence of boredom if not given a challenging environment. Their colors change to express emotion.
This article included lots of information about octopuses that was new to me. For instance, they have neurons in their arms. A freshly detached tentacle will even carry out purposeful movements as if it has a mind of its own. These creatures taste as well as feel with their suckers and effectively “see” with their skin.
Unfortunately, octopuses have one disadvantage as models for intelligent extraterrestrials: They die immediately after reproducing. Of course, your ET cephalopods don’t have to meet that fate. On the other hand, think of the plot-driving conflicts that could arise if an intelligent creature had to choose between mating and living out a full lifespan.
The article mentions that octopus intelligence and ours must have evolved completely independently from each other. In that respect they’re like aliens living on our own world but in an environment (the ocean) where our kind of life can’t survive without protective gear—like outer space or a non-Earthlike planet.
Margaret L. CarterCarter's Crypt