Page 137 - World of Animals - Book of Sharks & Ocean Predators

Narwhals
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How the tusk works

Far more than an overgrown tooth, the narwhal’s tusk is actually a highly
receptive sensory organ, guiding the creature through the icy waters

Peripulpal layer
Cementum
Spiral pattern This calcified substance that covers the entire tusk A unique feature in narwhal tusks, this layer is

All narwhal tusks spiral anti-clockwise, but is usually very tough, but in the narwhal it contains where the nerve cells that take information to the
scientists still don’t know why this is. less mineral content and is flexible. brain connect to the sensory tubules.

External conditions
Thousands of tubule openings on the surface of
the tusk are continually exposed to seawater and
everything contained within it.
Dentine
This strong layer of the tusk
contains protein, minerals and
is also punctuated by millions of
sensory tubules.
Pulp
This part of the tusk contains the nerve
cells that transfer the sensory signals
to the narwhal’s brain, enabling it to
effectively read its environment.

Sensing cells
At the base of the tubule,
these cells detect the
changes and properties
of the water near the
tusk’s surface.

Nerve network
Nerve cells contained within
Tubule openings the middle of the tusk relay
As many as 10 million tubules run from the information from the tusk
the centre of the tusk to the surface. to the brain.
ABOVE A microscopic view of the tubules on a narwhal tusk
at 1,000x magnifi cation strength

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