Cuttlebone

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.

Depending on the species, cuttlebones implode at a depth of 200 to 600 metres (660 to 1,970 ft). Because of this limitation, most species of cuttlefish live on the seafloor in shallow water, usually on the continental shelf.

The largest cuttlebone belongs to Sepia apama, the giant Australian cuttlefish, which lives between the surface and a maximum depth of 100 metres.

In the past, cuttlebones were ground up to make polishing powder, which was used by goldsmiths. The powder was also added to toothpaste, and was used as an antacid for medicinal purposes or as an absorbent. They were also used as an artistic carving medium during the 19th and 20th centuries.

Today, cuttlebones are commonly used as calcium-rich dietary supplements for caged birds, chinchillas, hermit crabs, reptiles, shrimp, and snails. It is not for human consumption.

Because cuttlebone is able to withstand high temperatures and is easily carved, it serves as mold-making material for small metal casting for the creation of jewelry and small sculptural objects.

...
Wikipedia