In A Nutshell
Everyone is familiar with the viscous mouth of a great white shark filled with razor-sharp teeth ready to rip into unsuspecting fish, marine mammals, and the occasional unwitting surfer. But it’s not just their mouths that are toothy: Sharks, skates, rays, and some other fish have teeth-like scales covering their bodies.
The Whole Bushel
Most fish in the world are covered in scales. Scales are designed to provide protection to fish and allow for free movement while swimming. But some fish are in a class known as “cartilaginous fish.” Instead of bones, these fish have cartilage keeping their bodies’ internal structures in line. Cartilaginous fish are also unique because they don’t have regular scales, but rather dermal denticles that wrap their bodies.
“Dermal denticles” roughly translates to “skin teeth” and rightly so. Their composition closely resembles that of “mouth teeth.” Just like our own teeth, dermal denticles have a vascular pulp center, a middle made of dentine, and an outer layer composed of enamel. In other words, they can bleed and may be able to sense pain.
Dermal denticles are typically very small and by looking with the naked eye, it may look like the fish has smooth, uniform skin. Under a microscope, however, things look very different. Dermal denticles grow from the outer layer of skin like scales, but unlike scales, they grow to a predetermined size and then stop. Then a new layer of denticles will grow on top of and in between the previous layer, providing a form of aquatic armor.
Sharks’ dermal denticles provide benefits that most scales do not. Due to their composition, it is believed that they provide better thermoregulation than regular scales. In addition, the grooved surfaces of the denticles allow sharks to swim with less resistance in the water. This means the sharks can swim faster and create fewer disturbances which might scare prey away. The design works so well that swimsuit manufacturers are now employing a similar design in their best racing suits.