Cuttlefish - the shapeshifters
Contributed by Wandy Hochgrebe
The name of this most beautiful and fascinating creature is a bit
confusing, since it is not a fish at all. The cuttlefish belongs to the
Phylum Mollusca, Class Cephalopoda (literally: head-footers) and is
closely related to the octopus and squid.
Like squids, but unlike the octopus, the cuttlefish has ten
arms. Two of those are rolled up into pouches located in the cheeks and
are adapted for capturing their prey. After finding a prey, the two
feeding tentacles shoot out to capture it. Holding on with the other
eight arms and their beak the cuttlefish's radula (tongue with
many little teeth) is used to get to the digestible parts of the prey
animal. Their diet mainly consists of shrimp, crab and fish.
moving their back fins in a wave-like motion the cuttlefish is able to
move slowly back or forwards. The internalised shell, the cuttlebone,
controls their buoyancy. By filling this porous 'backbone'
with gas or releasing gas, the cuttlefish can regulate its buoyancy.
After the animal dies the surfboard-shaped cuttlebone is washed
The eyes of a cuttlefish are highly developed and work
similarly to that of humans. Cuttlefish are able to distinguish between
different shapes of an object. They can't, however, see colour.
To escape the attention of
predators, cuttlefish will first try to blend in with their environment.
Tiny organs in their skin called chromatophores and the underlying
reflecting cells enable the animal to change colour rapidly or use the
ambient light by reflecting it to blend in with its environment. It is
also able to change the structure of its skin taking on the appearance
of sessile growth. This behaviour is called crypsis.
combinations of rapid colour changes, change of skin structure and
positioning of arms are also used as a form of communication between
cuttlefish themselves to either protect its territory or to impress a
potential partner. Figure 1 shows a good example of a cuttlefish
Once detected, the cuttlefish can
escape from predators by rapidly burrowing into the sand, using the
water-jet from the mantle funnel, or emitting a distracting puff of ink
to cover a retreat. The ink not only can confuse the predator by
creating a phantom prey, but it also contains chemicals which might
block or desensitise the senses the predator uses to detect the
Although the cuttlefish are solitary,
during mating season you will see many couples. The male produces sperm
packages, called spermatophores, which are transferred to the
female's oviduct back in the mantle cavity during and intense
embrace whereby the couple swims head-to-head through the water. After
fertilisation, the female lays round, white, yolky eggs on a sponge,
gorgonian or any vacant position that is well washed by the current to
ensure an adequate supply of oxygen for the developing young (See photo
for cuttlefish eggs deposited on the ceiling of a small cave). After
one month the eggs hatch and the juvenile cuttlefish drifts with the
current until it finds a reef on which to live.
The adult animals
normally die after the mating process and their surfboard shaped
cuttlebone washes ashore.
Article by Wandy Brouwer - Photos by Tim Hochgrebe from PLANULA Divers Retreat in Byron Bay