Is this for steering, or just to damage you if you rub them up the wrong way?
With thanks to Matt Ridley’s Twitter feed.
According to a commenter, these are “dermodenticles”, but google asks: Did you mean dermal denticles?
According to this:
These denticles decrease drag and turbulence, allowing the shark to swim faster and more quietly. Olympian swimsuit designers have taken a page from the shark’s playbook and created a fabric that mimics the exact proportion of the shark’s denticles, hugely improving a swimmer’s speed.>
Blog and learn.