Clams and other aquatic species that live their lives between a pair of hard shells are generally not thought of as having a means of visually sensing the world around them, but for at least one member of the group, that isn’t the case. Off the Pacific coast of North America lives the rock scallop (Crassedoma giganteum), a clam-like organism that grows attached to hard surfaces – and have eyes! Not content with just a pair of eyes, the rock scallop sports perhaps a couple of dozen eyes.
These eyes can’t form images the way our eyes can, but they allow the scallop the chance to detect changes in the brightness of light. This can be a benefit when you need to open your protective shells to pump water over your gills and to filter tiny particles of food out of the water, thus exposing soft parts of your body to potential predators. When a predator or even a non-threatening photographer approaches a scallop at least some of the light falling on it will be blocked. This change in the brightness of light is a signal that something is approaching. Taking the better safe than sorry approach, the scallop closes it shells, protecting the soft tissues that were exposed.
In today’s photo you can see the eyes as tiny yellow balls with a black dot in the center lining the edges of the orange mantle tissue protruding out between the two shells. At least 13 of these eyes are visible in the photograph.
This photo was taken with a Canon EF100 mm f/2.8 macro lens attached to both a Canon EF12 mm and EF25 mm extension tube on a Canon EOS 5D Mk. III in an Ikelite underwater housing. Light was provided by two Ikelite DS-161 strobes in eTTL exposure mode. The exposure was set to 1/45 sec. at f/9.5 and ISO 200.