Scientists discovered that the eyes of the whale shark is covered with thousands of placoid scales in the form of oak leaves — probably, they protect eyes from mechanical damage. In addition, when approaching objects eyes the whale sharks are drawn into the skull. The authors of the work published in the journal PLoS ONE, suggest that such protection of the eyes indicates that vision plays in the life of sharks a big role.
Eyes should be on the surface of the body, and because of this they are particularly vulnerable to chemical and mechanical damage. Animals protect the eyes in various ways, for example, many terrestrial and aquatic animals there are three ages: in addition to the usual two skin folds they have the nictitating membrane, that covers the eye lengthwise. Sharks have a nictitating membrane is protected additionally dermal denticles, and some cartilaginous fishes, which have no third eyelid, pull the eye in the skull or screw them in the sockets.
Scientists from the U.S. and Japan under the leadership of Taketeru Tomita’s (Taketeru Tomita) from the Research center Torashima in Okinawa studied the mechanism of protection of the eyes of whale sharks Rhincodon typus. The eyes of these animals are located at the sides of the head and issued outside of the eye sockets, which makes them particularly vulnerable. The researchers conducted a CT scan of the eyeball was extracted from dead sharks, and two live shark in Churaumi aquarium eye movements were videotaped and recorded using the ultrasonic sensor.
On the surface of the eye around the iris of the shark was about three thousand jagged placoid scales that are similar to oak leaves. On the surface of the body of a whale shark scales another form (with triple crests), and the split teeth are typical for Raznatovic sharks — first serve mainly to reduce water resistance, and the second for mechanical protection. Probably, scales are replaced whale sharks eyelids and protect the eye from mechanical damage. Such eye protection is still not found in other cartilaginous fish, including whale sharks close species.