Super fast color changes, mysterious eyes and a spectacular mating ritual. The cuttlefish is an unusual animal. It has a large internal shell as backbone, which serves for improving buoyancy as well as sturdiness. You often find these cuttlebones on the beach. They are sold in pet stores as a source of calcium for caged birds. Cuttlefish are easily frightened; it is difficult to display them in a Sea Aquarium. The common cuttlefish is very common in the North Sea, down to a depth of around 150 meters. In the spring, it migrates via the English Channel to coastal waters to reproduce.