These beautiful creatures have been around for 400 million years. Nautilus shells have a series of chambers connected by the siphuncle - a tube made of tissue. The chambers contain a mixture of gas and seawater, and the siphuncle regulates how much of each is present within the chambers at any given time.

If a nautilus wants to go deeper, the siphuncle makes that happen by pumping sodium and chlorine ions into the chambers. Extra water then enters these compartments thanks to osmosis, making the animal less buoyant, and the nautilus sinks. To reverse this process and travel upward, the siphuncle simply removes ions from the chambers, and water consequently flows into the mantle cavity. As it leaves, gas bubbles start to diffuse, which lightens the shell.

Dimensions: W 15.2 x 15.2 x H 28cm