The image above shows a live chambered nautilus, a cephalopod found deep in the waters of the western Pacific Ocean. The nautilus shell is divided by transverse septa into internal chambers, and the animal lives only in the last chamber. These chambers are connected by a cord of living tissue called the siphuncle.  When a chamber is abandoned, its fluid is removed and replaced with gas by the siphuncle, helping to compensate for the added mass of the shell and body, thereby maintaining buoyancy.  To see a sectioned chambered nautilus shell, click here.