Which marine animal has a shell divided into camera-like chambers?

The chambered nautilus has a shell divided into camera-like chambers.

As the nautilus grows, it adds a new chamber to the outer edge of its shell and moves its body into that newest space. Older chambers remain behind and are connected by a living tissue tube called a siphuncle. The animal adjusts gas and liquid in these chambers to regulate buoyancy.

The shell’s visible spiral records the animal’s growth. A mature chambered nautilus may have around 30 chambers, although the exact count varies with age and species. This internal structure is one reason nautilus shells are often compared with the shells of long-extinct ammonites.

The nautilus is a cephalopod, but unlike squid and octopuses it retains an external shell. Its tentacles lack the large suckers typical of many other cephalopods, and it has relatively simple eyes without a lens. Those differences make it a living window into ancient cephalopod history.