Japanese marine biologists have discovered that whale sharks, the world’s largest fish, have teeth-like scales adorning their eyeballs.

“We already knew that many sharks, including whale sharks, are covered with these denticles. However, finding them on the eyeballs of these fish is quite the surprise,” said study lead, Dr Taketeru Tomita from the Okinawa Churashima Foundation Research Centre. “The highly protected features of the whale shark eye seem to suggest the importance of vision in this species. This adaptation of the eye is a new mechanism of eye protection not seen in vertebrates until now.”

Having observed whale sharks in captivity and analysed CT scans, performed on a preserved whale shark eyeball, and ultrasounds from two captive whale sharks, the researchers extended their research into the mechanisms whale sharks use to retract their eyes. "It is likely that whale sharks maintain their vision during eye retraction because the pupils of the whale sharks were not completely covered with surrounding white tissues when their eyes retracted, though their visual field would be much more restricted than when their eyes are positioned normally," said Dr Tomita.

Eye denticles of a whale shark. Credit: Tomita el al

The full study was published in PLOS One.