Basic Anatomy Defined
Size and shape of the eyes vary between shark species. Some are elongated
while others are round. In some the pupil is a black slit, while in others the
pupils are obscured and the entire eye is black.
Another interesting note is that some sharks have a movable third eyelid called
a "nictitating membrane," which can completely cover and protect the eye. This
nictitating membrane is similar to that of the ordinary house cat.