It is a hard, brittle internal structure found in all members of the family Sepiidae, commonly known as cuttlefish, within the cephalopods. In other cephalopod families it is called a gladius. Cuttlebone is composed primarily of aragonite.
 
Cuttlebone (CB), the internal structure isolated from Sepiella maindroni de Rochebrune, is traditional Chinese medicine used in the treatment of stomach ulcers, gastric hyperacidity, and a variety of bleeding