These two nautiluses (Nautilus belauensis) are pictured off the coast of Palau in the Pacific Ocean. There are six living species of nautilus who live in chambered shells. As they get bigger, they move into a newly formed, larger section of the shell. The shell is not only used for protection, but as a way to control their movement and buoyancy. Its spiral shape is a natural example of Fibonacci's sequence, or a logarithmic spiral. Nautiluses are often caught for the beauty of their shells amidst growing concern for their sustainability.