Cuttlefish have an
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
liquid in its chambers. The cuttlebone of each
species has a distinct shape, size, and pattern of ridges or texture. Cuttlebones are used by
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
Cuttlefish are sometimes called the
chameleon of the sea because they are able to change their skin color. Their skin can flash a colorful pattern in order to
communicate with other cuttlefish and to
camouflage them from
predators. This color-changing function is produced by groups of red, yellow, brown, and black
chromatophores above a layer of reflective iridophores and leucophores. These are all in the cuttlefish's skin, and work together to change its colour. There are up to 200 of these special
pigment cells per square
The pigmented chromatophores have a sac of pigment and a large
membrane that is folded when retracted. There are 6-20 small
cells on the sides which can contract to squash the
elastic sac into a disc against the skin.
Iridophores are plates of
protein, which can reflect light. They are responsible for the metallic blues, greens, golds, and silvers often seen on cuttlefish. All of these cells can be used in combinations. As well as being able to influence the colour of the light that reflects off their skin, cuttlefish can also affect the light's
polarization, which can be used to signal to other animals which sense polarization.
Cuttlefish eyes are among the most developed in the animal kingdom. The way cephalopod eyes develop is fundamentally different from that of
vertebrates like humans, but the way they work is rather similar.
 The similarity between cephalopod and vertebrate eyes is an examples of
convergent evolution. Although they cannot see color, they can perceive the polarization of light, which improves their ability to see contrast. They have two spots of concentrated sensor cells on their retina (known as
fovea), one to look more forward, and one to look more backwards. The lenses, instead of being reshaped as they are in humans, are instead pulled around by reshaping the entire eye in order to change focus.
Pfeffer's Flamboyant Cuttlefish, from
The blood of a cuttlefish is an unusual shade of green-blue because it uses the
haemocyanin to carry
oxygen instead of the red
haemoglobin that is found in
vertebrates. This is similar to the blood of
arthropods. Haemocyanin is not so good at carrying oxygen as is haemoglobin. The blood is pumped by three separate '
hearts'. Two of these are used for pumping blood to the cuttlefish's pair of
gills (one heart for each gill), and the third for pumping blood around the rest of the body.