If looks could kill: Giant whale sharks have teeth on their eyeballs, study finds
Whale sharks — which grow to an enormous 40 feet — have teeth on their eyeballs, according to a new study titled “Armored eyes of the whale shark.”
They also have retractable eyeballs, the same study found.
However, it’s not a case where looks can kill.
The teeth, called dermal denticles, are not for biting, but serve instead as “a defense mechanism,” states the report published Monday in PLOS ONE.
Scientists at the Okinawa Churashima Research Center in Japan even went so far as to count the denticles on one whale shark’s eye and found 2,900 “around the iris,” the report says.
“Whale sharks lack eyelids,” the report states. “Thus, the covering of the eye surface with denticles in the whale shark is probably useful in reducing the risk of mechanical damage to the eye surface.”
ReefQuest Centre for Shark Research notes the term dermal denticles translates “literally (to) tiny skin teeth.”
The same denticles have so far not been found in the eyes of species closely related to whale sharks, the report says. But other sharks, including the great white, have a different type of denticle on their skin that is often mistaken for scales, according to the Smithsonian National Museum of Natural History.
“Shark skin is covered by tiny flat V-shaped scales, called dermal denticles, that are more like teeth than fish scales,” the museum reports. “These denticles decrease drag and turbulence, allowing the shark to swim faster and more quietly.”
As for the ability to retract their eyeballs, the study found it was more than just a subtle change. Researchers calculated that whale sharks could retract their eyes by more than 50% of the eyeball diameter, and do it for days at a time, the study said.
They also found this retraction was “accompanied by eye rotation,” the report states.
“Because of the relatively small eyes (eye diameter less than 1% of total length), it has been assumed that the whale shark depends little on vision compared with other senses,” the study says. “However, the highly protected features of the whale shark eye, in contrast to the traditional view, seems to suggest the importance of vision in this species.”
Whale sharks are considered the ocean’s biggest fish and are known as filter feeders, despite their intimidating name, according to The Florida Museum.
“They gulp in water and filter everything from plankton and fish eggs to crustaceans and schooling fish, to occasional larger prey like squid or tuna,” the museum reports. “Despite their size, they are considered harmless to humans, and will often interact docilely with divers.”
