Chambered nautilus (Nautilus pompilius)
A newly hatched nautilus wears a shell divided into four small chambers. As a nautilus grows, it gains more living space by building new chambers connected to the old ones; adult shells have 30 chambers. To control its buoyancy, a nautilus pumps fluids in and out its shell chambers, which are connected by tubes called “siphuncles.”
A nautilus swims using jet propulsion—it expels water from its mantle cavity through a siphon located near its head. By adjusting the direction of the siphon, a nautilus can swim forward, backward or sideways.