Cuttlebone
（重定向自Cuttlefish bone）
![Top and bottom view of a cuttlebone, the buoyancy organ and internal shell of a cuttlefish](/Images/godic/202501/07/Cuttlefish-Cuttlebone24708.jpg")
![](/Images/godic/202501/07/Cuttlefish-Cuttlebone14708.jpg")
![Cuttlebone of Sepia officinalis (left to right: ventral, dorsal, and lateral views)](/Images/godic/202501/07/Herklots_1859_I_2_Sepia_officinalis_-_schelp4708.jpg")
![Common cuttlefish Sepia officinalis](/Images/godic/202501/07/Sepia_officinalis-f4708.jpg")
Cuttlebone, also known as cuttlefish bone, is a hard, brittle internal structure (an internal shell) found in all members of the family Sepiidae, commonly known as cuttlefish, a family within the cephalopods.
Cuttlebone is composed primarily of aragonite. It is a chambered, gas-filled shell used for buoyancy control; its siphuncle is highly modified and is on the ventral side of the shell. The microscopic structure of cuttlebone consists of narrow layers connected by numerous upright pillars.