Do Whale Sharks Have Teeth on Their Eyeballs?

The Short Answer

Yes — whale sharks have approximately 2,900 tiny tooth-like structures called dermal denticles covering each eyeball, and they can retract their eyes fully into their sockets in under one second.

What Are Dermal Denticles?

Dermal denticles are the microscopic, tooth-shaped scales that cover the skin of all sharks. They give shark skin its famously rough, sandpaper-like texture and reduce drag as the animal moves through water. What makes whale sharks extraordinary is that these same structures don’t just cover their bodies — they form a continuous armoured shield directly over each eye. Scientists confirmed this in 2020 using micro-CT scanning technology, which allowed researchers to map the denticle structures in three-dimensional detail. It was a discovery that surprised the marine biology community, as nothing quite like it had been documented in any other vertebrate.

Why Do Whale Sharks Have No Eyelids?

Most vertebrates protect their eyes with eyelids, nictitating membranes, or both. Whale sharks have none of these. Instead, evolution took a radically different path, repurposing the same biological toolkit used to build shark skin and redirecting it toward eye protection. The denticle armour on the eyeball serves the same function an eyelid would — shielding the sensitive surface of the eye from physical damage, debris, and potential threats in the water column. It is one of the most unusual adaptations in the animal kingdom, and it exists in the largest fish on the planet.

The Eye Retraction Mechanism

The armoured eye isn’t the only trick whale sharks have. When threatened or when an object comes too close, a whale shark can pull its entire eyeball back into its socket in under one second. This retraction is controlled by a set of muscles that essentially allow the eye to disappear on command. The micro-CT scanning research that identified the denticle shield also mapped this retraction system, revealing how the eye rotates and recedes when engaged. The combination of external denticle armour and the ability to fully withdraw the eye gives whale sharks a level of ocular protection that has no parallel in the vertebrate world.

How Big Are Whale Sharks?

Whale sharks are the largest fish alive on Earth today, reaching lengths of up to 18 metres and weights of around 19 tonnes. Despite their size, they are filter feeders — they cruise through the water with their enormous mouths open, filtering plankton, small fish, and fish eggs. Their gentle nature makes them a popular subject for divers and marine researchers alike. But as the eye denticle discovery shows, there is still a great deal about these animals that science is only beginning to understand.

Why Was This Discovered So Recently?

Whale sharks are rare, hard to study, and logistically difficult to examine up close in controlled conditions. Detailed imaging of soft tissue structures like eyeballs requires technology such as micro-CT scanning, which became widely accessible to marine biologists relatively recently. The 2020 study published in PLOS ONE was the first to systematically image and describe the denticle shield, and it opened new questions about how widespread similar adaptations might be across the broader shark family tree. The ocean remains one of the least explored environments on Earth, and discoveries like this are a reminder of how much is still waiting to be found.