A nautilus is a sea creature with a beautiful spiral shell divided into chambers. As the nautilus grows, it builds new, larger chambers and moves forward into them, sealing off the old ones behind. The innermost chambers fill with gas, helping the nautilus float and move up and down in the ocean like a submarine adjusting its buoyancy.

The nautilus has existed with a similar basic body plan for hundreds of millions of years, making its group older than dinosaurs, older than trees, even older than insects. Scientists call animals like this living fossils because they've survived so long while most other ancient creatures went extinct.

The shell's spiral follows a mathematical pattern called a logarithmic spiral, where each chamber grows proportionally larger than the one before it. Artists, architects, and mathematicians have studied the nautilus shell for centuries because its growth pattern appears throughout nature, from galaxies and hurricanes to the curl of a fiddlehead fern.

In Jules Verne's novel Twenty Thousand Leagues Under the Sea, Captain Nemo names his submarine the Nautilus after this remarkable creature, a vessel that moves gracefully through the ocean depths, just like its namesake.