A cuttlebone, what's left of the cuttlefish, washed up on the shore.

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The cuttlefish's looks much like a 's beak, but it is hard to see because it lies buried at the base of the animal's eight arms. The cuttlefish can use its beak to help subdue prey and to defend itself against predators and rivals by biting. Like cuttlebones, beaks differ among species, and their remains enable scientists to identify which cuttlefish species have lived and died in certain areas.
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Cuttlefish is neither squid nor octopus but belong to the class Cephalopoda, which also includes squid, octopuses, and nautiluses. ‘Cuttle’ is a reference to their unique internal shell, the cuttlebone. Despite their name, cuttlefish are not fish but mollusks. They are not cuttlebone, they are cuttlefish bone.
Photo provided by FlickrThe largest cuttlebone belongs to , the giant Australian cuttlefish, which lives between the surface and a maximum depth of 100 metres.
Photo provided by FlickrCuttlebone, also known as cuttlefish bone, is a hard, brittle internal structure (an internal shell) found in all cuttlefish.
Photo provided by Flickr
Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda (which also includes squid, octopuses, and nautiluses). Despite their name, cuttlefish are not fish but molluscs. Cuttlefish have an internal shell (the cuttlebone), large W-shaped pupils, and eight arms and two tentacles furnished with denticulated suckers, with which they secure their prey. They generally range in size from 15 cm (5.9 in) to 25 cm (9.8 in), with the largest species, Sepia apama, reaching 50 cm (20 in) in mantle length and over 10.5 kg (23 lb) in weight.[1] Cuttlefish eat small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. Their predators include dolphins, sharks, fish, seals, seabirds and other cuttlefish. Their life expectancy is about one to two years. Recent studies indicate that cuttlefish are among the most intelligent invertebrates.[2] Cuttlefish also have one of the largest brain-to-body size ratios of all invertebrates.Cuttlebone is the chalky internal shell of a ten legged,
squid-like mollusk known as the cuttlefish. It has a hard, thin
crust on the outside which surrounds the internal softer
shell. The soft side is composed of a calcium carbonate and
is almost pure calcium. Domestically, the bone is used by
parakeets and canaries as a bill sharpener and can be
purchased at most pet stores. In powdered form it is used
as a polishing agent.
Today, cuttlebone casting is mostly used by artists and craftsman. I
absolutely love the spontaneity of the process. There are numerous ways to
create a mold for cuttlefish casting. The procedure outlined is the direct
method of carving into the bone. This is a simple, low-tech process which can
be completed from start to finish in less than an hour.
The other way deals with metalworking. Cuttlefish have a hard calcium rich structure known as the cuttlebone within them. It is porous and light and in life provides a source of buoyancy. Harvested, the cuttlebone has a number of uses. Pet owners may recognize it as a cheap calcium source for their birds or rodents and it is commonly sold in pet stores. Silversmiths, on the other hand, prized it for casting. The cuttlebone is easy to carve and cut, but can resist very high temperatures with no problems. Jewelers will carve out the shape they want to form then fill the resulting cavity with molten metal. They then simply wait for the silver to cool, then remove it. This technique is both simple and old; silver belt buckles have been found in Baden-Württemberg, Germany, that were cast in cuttlebone sometime around the six or seventh century.