Squids possess a stiff structure known as a pen, that acts as a flexible backbone. Their blood is this colour because they use an oxygen-carrying molecule in their blood that contains copper. Octopuses and squids have hard, parrot-like beaks. These are excellent for killing, and tearing pieces of flesh from their prey. Octopuses live in dens on the sea floor.
Squids live in the open oceans.
Octopuses use their eight sucker-lined arms to capture their prey and move about on the ocean floor. Squids have eight arms lined with suckers and two specialized tentacles that they use to reach out and capture prey. Octopuses eat bottom-dwelling crustaceans. Squids eat fishes and shrimps. Some deep water squids may be scavengers.