The "cuttlebone" is a unique internal shell found in cuttlefish,
which are actually mulloscs, not fish.
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weeds
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A cuttlefish has a solid, bone-like structure, known as a
cuttlebone. This can be carved easily, and one application is to
make a casting mould out of it.
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Cuttlefish bone, sometimes known as cuttlebone and used as a
source of calcium for caged animals, is 85.0% Calcium
Carbonate.