Shark skin under a microscope.
Shark skin doesn’t look like normal fish skin. It’s made of microscopic diamond shaped scales with rough edges, called “denticles”. These are thought to share an evolutionary origin with teeth - indeed, they have much more in common with teeth than with scales. Like teeth, they consist of a central cavity made of pulp surrounded by dentine and enamel.
The flexible but irregular surface is impossible for barnacles and other micro-organisms to cling to, as well as decreasing drag and turbulence.
So just when you thought sharks couldn’t get any scarier, it turns out that their entire bodies are literally COVERED with teeth.