One of the most mystifying creatures of the deep, the cuttlefish has abilities and
even senses that are alien to us humans. This versatile animal can change its
appearance at will, mimicking floating vegetation or rocks on the seafloor. Yet
when danger looms, the animal can jet away at great speeds, shooting out a
smoke screen of ink or using its ink to create decoys of itself. How does the
cuttlefish accomplish all this? Below, take a look at select
parts of this octopus relative and learn more about how this master of
deception and disguise functions.—Rima Chaddha
Both the arm (top) and
the tentacle (bottom) are lined with suckers.
Arms and Tentacles
the octopus's arms, which that animal often uses to move and carry
objects, the cuttlefish's eight arms are specialized for grasping prey
after the cuttlefish captures it with its two elongated tentacles. When
potential food sources such as fish or shrimp swim near, the cuttlefish can
alter the color of its skin while waving its arms in a mesmerizing display.
This lures potential prey to within reach of the cuttlefish's tentacles,
which can then shoot rapidly from a pocket at the base of the arms to grab the
prey. The arms are also important for a defensive display in which the
cuttlefish sucks water into its mantle cavity and spreads its arms in order to
appear larger to its potential opponent.
The dark area seen here
is part of the cuttlefish's strong, sharp beak, the rest of which lies
behind the buccal (cheek) mass.
cuttlefish's beak looks much like a parrot'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.
Unlike in mammals, the cuttlefish's optic lobes are located outside of its cartilage brain casing. Above, a transverse cross-section of the cuttlefish brain.
cuttlefish has one of the largest brain-to-body size ratios of any
invertebrate, perhaps even larger than that of the octopus. The cuttlefish
brain can handle input from a variety of senses, including sight, smell, and
even "sound" (in the form of pressure waves). According to some
scientists studying cephalopod learning, the cuttlefish can use visual clues to
solve mazes, making it as intelligent as the octopus or land animals like the
The rigid cuttlebone
allows the cuttlefish to keep a constant internal volume, unlike a fish's
swim bladder, which expands and contracts with depth.
defining characteristic of the cuttlefish, the cuttlebone is a porous internal
shell that helps control buoyancy, making it functionally similar to swim
bladders in fish. Cuttlebones have both gas-filled forward chambers and
water-filled rear chambers. Although it can take hours for the cuttlefish to
change its density through its cuttlebone alone, the animal can control its
positioning in the water with the aid of its specialized fins and mantle. The
cuttlebone is rich in calcium and is often sold in pet stores as a nutritional
supplement for birds.
A cuttlefish looks on
through its large eye. Note the clear "W" shape of its pupil.
color-blind, the cuttlefish has two of the most highly developed eyes in the
animal kingdom. It can see well in low light and can also detect polarized
light, enhancing its perception of contrast. While we humans reshape our lenses
in order to focus on specific objects, the cuttlefish moves its lenses by
reshaping its entire eye. Also, the cuttlefish's eyes are very large in
proportion to its body and may increase image magnification upon the retina,
while the distinct "W"-shaped pupil helps control the intensity of
light entering the eye.
undulating fins can move more freely than fish fins because they lack both bony
and cartilaginous supports.
the cuttlefish uses its mantle cavity for jet propulsion, it relies on its
specialized fins for basic mobility and maintaining consistent speeds.
Resembling a short, flouncy skirt, the muscular fin can maneuver the cuttlefish
in nearly any direction: backward, forward, even in circles, with such movement
being more energetically efficient than jetting. The movement and positioning
of the fins also come into play when
smaller males in certain species mimic the opposite sex in order to swim past larger
males and gain access to females.
The cuttlefish's pair of orange gills (one appears above) filter oxygen from
seawater and deliver it to the bloodstream.
Hearts, and Blood
cuttlefish has three hearts, with two pumping blood to its large gills and one
circulating the oxygenated blood to the rest of its body. The blood itself is
blue-green in color because it possesses hemocyanin, a copper-containing
protein typical in cephalopods—cuttlefish, octopuses, and
squids—that transports oxygen throughout their bodies. (Mammals'
red blood uses the iron-rich protein hemoglobin to do the same thing.)
The dark ink sac can be
seen clearly in this image of part of the mantle cavity.
its close relatives, the squid and octopus, the cuttlefish is equipped with an
ink sac that can help it make a last-ditch escape from predators that
hunt by sight. The cuttlefish can eject its ink in two ways. One way creates a
smoke screen behind which the animal can escape perceived danger. In the other,
the released ink takes the form of "pseudomorphs," or bubbles of
ink surrounded by mucus that are roughly the size of the cuttlefish and can act
as decoys. The ink, which contains dopamine and L-DOPA, a precursor to
dopamine, may also temporarily paralyze the sense of smell in predators that
hunt by scent.
In this scanning
electron microscope image, "L1" and "L2" mark the
lateral lines, while "A" indicates the cuttlefish's arms.
the cuttlefish can't hear, it can detect sound in the form of pressure
waves using its lateral epidermal lines. Seen here via a scanning electron
microscope, these lines consist of thousands of hair cells. The cells seem to be especially sensitive to sounds ranging
between 75 and 100 Hz, with 100 Hz being similar in frequency to a typical
automobile engine running at maximum speed. One physiological study showed that
in total darkness, healthy cuttlefish could capture about 50 percent of
available prey, whereas cuttlefish with compromised epidermal lines could
capture only about 30 percent. The hair cells can also be used in defense,
allowing cuttlefish to detect the movement of possible predators.
In this view of the
inside of an adult cuttlefish's mantle, the orange gills and dark ink sac
are clearly visible.
multifunctional mantle cavity is important for cuttlefish locomotion, giving
the animal its characteristic jet propulsion ability. To jet away from a
predator, the cuttlefish sucks water into the cavity and then uses its strong
mantle muscles to expel the liquid with great force, driving the cuttlefish in
the opposite direction. Water exits through a movable part called the funnel,
which controls the angle of the spray. The mantle cavity also aids in
respiration by bringing water to the animal's gills, which in turn filter
oxygen into its bloodstream.
Males and females face
each other and embrace while mating.
mating, the male uses a modified arm to transfer his genetic material into the
female's buccal area. This is the part of the female's mouth that
stores the male's spermatophores (sperm packaged in special containers)
until she is ready to use them to fertilize her eggs. Because the female often
accepts more than one mate, the male sometimes sprays water through his mantle
funnel into the female's buccal area to wash out other males'
spermatophores. When she is ready to deposit her eggs in safe locations such as
under rocks or in discarded shells, the female uses her arms to wipe the stored
spermatophores onto each egg.
Stripes ripple across a cuttlefish's skin. To see another example, go to "Quick Change Artists" elsewhere on this Web site.
When it comes to changing one's skin color, the cuttlefish outshines even the chameleon, in both degree and kind. Its skin possesses up to 200
chromatophores (pigment cells) per square millimeter, allowing the animal to
pattern itself with a variety of colors. When vying for a mate, for example,
some male cuttlefish will showcase "intense zebra displays" (see
left). The cuttlefish can also use muscles in its dermis to change its skin
texture from smooth to rough, enabling it to hide easily among rocks on the
seafloor, for instance.