A Telescope in a Shell
Along the mantle of a single scallop, up to 200 tiny, bright blue eyes peer out into the aquatic world. These are not simple light-sensing pits. Each one-millimeter-wide eye is a fully functional reflecting telescope, parallel to the segmented mirror telescopes used in modern astronomy. While most animals, including humans, use a lens to refract and focus light, the scallop uses a concave mirror at the back of its eye to reflect light onto its retinas.
The mirror is a living structure. It is built from millions of perfectly square, flat crystals of guanine, the same molecule that forms one of the building blocks of DNA. The scallop exerts precise biological control to shape the guanine into squares—a form not typically found in nature—and tiles them together with minimal distortion. The crystal tiles are arranged in 20 to 30 layers, separated by cytoplasm, to create a highly reflective surface. The entire structure is tuned to reflect blue-green light around a wavelength of 500 nanometers, the light that best penetrates its seafloor habitat. The local Spiny Scallop (Chlamys hastata) and Weathervane Scallop (Patinopecten caurinus) found in these waters have this visual system.