The iridescent blue eyes of the Doughboy Scallop, (Mimachlamys asperrima), are little optical marvels. They are in fact more like tiny Schmidt telescopes than conventional eyeballs.
The back surface of the scallop’s eye is like a mirror which reflects the incoming light back towards the lens opening. The light sensitive cells of the retina are on the back of the lens and not the eyeball so they actually sense the reflected image back off the mirror.
As far as eyeballs go they are are quite rudimentary and not much more than a pin-hole lens. The internal mirror structure however gives the primitive eye a huge light gathering advantage important for dim lighting conditions, sufficient to detect the approach of predators in near darkness.
Despite their amazing biology, from my point of view those alluring blue eyes are just stunning.
Photo: Robert Rath, ‘The Scallop’s Eyes’ 1/200s f/22 ISO100 100mm