The chambered or pearly nautilus is a cephalopod (a type of mollusk)—a distant cousin to squids, octopi, and cuttlefish. Unlike its color-changing cousins, though, the soft-bodied nautilus lives inside its hard external shell. The shell itself has many closed interior chambers or “compartments.”The animal resides in the shell’s largest chamber, while the other chambers function like the ballast tanks of a submarine. This is the secret to how the nautilus swims. The tissue in a canal called the siphuncle [sigh-funk-el] connects all of the interior chambers. As seawater pumps through the living chamber, the nautilus expels water by pulling its body into the chamber, thereby creating jet propulsion to thrust itself backwards and to make turns. While swimming up or down through the water column, the nautilus uses its siphuncle to suck fluid into, or draw it out of, the smaller sealed chambers, allowing the animal to adjust its overall buoyancy