Cuttlefish
Cuttlefish have an internal cuttlebone, made of calcium carbonate. It is porous, full of small holes, The buoyancy of the cuttlebone can change, allowing the cuttlefish to go lower or higher by changing the amount of gas and liquid in its chambers. The cuttlebone of each species has a distinct shape, size, and pattern of ridges or texture. Cuttlebones are used by jewellers and silversmiths as moulds for casting small objects. They are probably better known today as the material given to pet birds as a source of calcium. The cuttlebone is only found in cuttlefish, and is one of the features that makes them different from squid and other molluscs.