Page 20 - Shark

Blue shark’s
nictitating Making sense
eyelid Sensory
pores

Sharks have the same five senses as people—
they can see, hear, smell, taste, and touch.
There is also a sixth sense that Metal detector
allows sharks to detect weak, Sweeping a metal
electrical signals generated by detector back and forth
to find buried metal
their prey. This electro-sense objects is like the
way hammerheads
may also help them to navigate (pp. 42–43) hunt for
on their journeys in the sea. This underwater fish hiding in the sand.
Nostril world is quite different from our own. Light levels
decrease with depth and colors fade to blues. Sound travels five times
GoinG to its head
Like us, a shark’s major sense organs are on faster and farther. Odors are dissolved in water, not wafted in the
its head. Seen on this blue shark are the eye, air. Sharks can detect vibrations made by animals moving through
nostril, and sensory pores, which detect weak
electric signals. The eye is partly covered by a the water, giving them the sense called “distant-touch.” It is hard
third eyelid, called a nictitating (or blinking)
eyelid, which protects the eye when the shark to find out exactly how a shark perceives its world, but studies on
attacks its prey or nears unfamiliar objects. As their behavior and how sense organs work give some idea about
the shark swims along, water flows through
the nostril beneath the tip of the snout, what it is like to be a shark.
bringing a constant stream of odors.
all kinds oF eyes
According to how
much light there is,
the iris in a shark’s
eyes contracts or
expands to alter the
size of the pupil. A
layer of cells at the
back of the eye, called
the tapetum, reflects
light back onto the
Epaulette’s slit-shaped pupil Dogfish with closed pupil retina, where images
are focused, making
maximum use of any
available light. This
FeedinG Frenzy helps sharks to see
When sharks are feeding on baits, they may become in dim light. Cats
overexcited and snap wildly at their food. They may also have a tapetum,
bite each other and even tear one another apart. which is why their
eyes reflect lights
shone at them. On
bright sunny days a
shark can shield its
Semicircular Angel shark’s pupil Reef shark with vertical pupil tapetum with a layer
canal, one of pigment. Like
of three humans, a shark’s
retina has two types
of cells—rods work
in dim light and are
sensitive to light
changes; cones resolve
details and probably
allow sharks to see
in color.

the inner ear
Sharks do not have external ear flaps, but Horn shark’s pupil Ray with light-blocking screen
have ears inside their heads on each side distant touch
of the brain case. Three semicircular canals A shark has a lateral line system running
placed at right angles to each other are like down each side of the body and onto its Starry smooth-hound
those found in the ears of all vertebrates. head. The lines are small Lateral line showing lateral line
These canals help a shark work out which canals with tiny pores
way it has turned in the water. Receptors in beneath which are cells
the inner ear, like those in the lateral line on with minute hairs. Scattered
the skin, pick up sounds traveling through the over the body are similar hair
water. Each ear has a small duct that leads to cells called pit organs which, like
a pore on the top of the shark’s head. the lateral lines, pick up vibrations.

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