Cuttlefish bone

Cuttlebone, also Known as Cuttlefish Bone, is a Hard, Brittle Internal Structure Found in all Members of the Family Sepiidae, Commonly Known as Cuttlefish.
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.[1] 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 2,000 Ft). Because of this Limitation, Most Species of Cuttlefish Live On the Seafloor in Shallow Water, Usually On the Continental Shelf