Whale sharks are fish that can grow as long as 59 feet (18 meters), so there's not much in the ocean that's going to mess with them. However, they are vulnerable in their own ways, and have developed adaptations to protect themselves from the friction of swimming, namely, teeth that grow all over their bodies, including their eyeballs! These modified teeth are called dermal denticles.
Whale sharks, unlike some other shark species, don’t have eyelids. Also, their tiny eyes are located at the corners of their square heads, exposing their peepers to potential damage. That’s where the protective eye denticles come in.
Sharks have dermal denticles elsewhere on their bodies. These marine animals don’t have scales like other fish, but they do have placoid scales, which are made of dermal denticles. These modified teeth, with their hard enamel, provide sharks with armor-like protection, but they also work to reduce friction in the water, helping sharks swim with speed and stealth.
A study of whale sharks from Japanese aquariums, both living and dead specimens, show the denticles comes in all sorts of shapes. One shark eyeball had nearly 3,000 denticles! Read more about this research at Gizmodo.
(Image credit: istolethetv)