Asian Diver – March 2018

Dermal

Denticles

Ampullae of

Lorenzini

Water

Gill slits

What Makes a Shark a Shark?

Sharks are a group of fish that first appeared around 420 million years ago and have since diversified into over 470 different

species that inhabit every ocean on our planet. Their size ranges from the tiny dogfish measuring only 17 centimetres to the

incredible whale shark, the biggest fish in the ocean, which can reach lengths of up to 12 metres and weigh over 20 tons.

Although these fish come in many shapes and sizes, they all share unique characteristics that make them a shark

Sharks are built for

speed and stamina,

and their skin is

perfectly designed

for this purpose

DERMAL DENTICLES

A shark’s skin is composed of hundreds of

tooth-like scales called dermal denticles.

These ‘teeth’ are what makes a shark’s

skin tough and also incredibly effective at

reducing drag

JAWS AND TEETH

Most sharks have multiple rows of teeth that continue to grow and replace the ones that are lost throughout their

lifetime. Much of what we know about sharks has been learnt from fossilised shark teeth, as unlike the rest of the

body, they can remain intact on the seabed for hundreds or even thousands of years

AMPULLAE OF LORENZINI
Located near the nostrils, around the head
and on the underside of the snout are small
jelly-filled pores. These sensory organs
are able to detect electrical fields underwater
and are used by sharks to help locate prey
and navigate

Pore surface

Electrical fields

Sensory cell

Some shark species
must swim continuously
to pass water over
their gills to breathe
while others use a
process called buccal
pumping instead

MULTIPLE GILL SLITS
Most species of sharks have five pairs of gill slits, but a
few have six and even seven, typically located on the side
of the head. Tiny membranes in the shark’s gills extract
oxygen from the water

Jaws

Cranium

A shark’s upper jaw is not fixed to the cranium, allowing the jaw to partially protrude from the head. The jaw is also supported by

plates called “tesserae” which give more strength and support where sharks need it most. This extra strength allows sharks to

grab and hold their prey, while larger species rip and tear their prey before swallowing