A cuttlebone is the internal shell of a cuttlefish, a sea creature related to squids and octopuses. Unlike the hard outer shells of crabs or snails, the cuttlebone sits inside the cuttlefish's body, providing structure and helping it control its depth in the water. The bone is filled with tiny chambers of gas and liquid that the cuttlefish can adjust, like a submarine using ballast tanks to rise or sink.

Cuttlebones have a fascinating chalky white appearance with a slightly ridged texture. When they wash up on beaches, they look like oval pieces of white foam or bone. People often collect them to give to pet birds like parakeets and cockatiels, who peck at the calcium-rich cuttlebone to keep their beaks trimmed and get important minerals.

The cuttlebone's structure is remarkably light yet strong, inspiring engineers who design lightweight materials for aircraft and buildings. Scientists study how cuttlefish evolved such an efficient internal support system, different from the backbones of fish or the hard shells of their mollusk relatives, like clams. If you visit a beach where cuttlefish live, you might spot these curious white objects among the seaweed and shells.