Cephalopods were a type of animal which included octopi and squids.
Throughout the universe, various cephalopod species existed. This was one of the many shapes that recurred throughout the universe, including insectoid and humanoid.
Ianto Jones told his very near-human boyfriend, Jack Harkness, a fear of a lover leaving him equally for "men, women, or cephalopods." (TWN: The House that Jack Built)