scallops have eyes, and there are many. These small eyes, only millimeters in diameter, are arranged on the mantle on the edge of their shells, sometimes in a beautiful sapphire blue.

if you often read this account, you may already know these things. Today we're going to go a step further and look at what's hidden in the scallop's eyes-a delicate little mirror.

in our own eyes, it is the convex lens structure that is responsible for focusing imaging, while the case of scallops is quite different. They also have lenses in their small eyes, but what really gathers light is a natural mini concave mirror that reflects light.

in the 1960s, researcher Michael Land observed this small mirror and pointed out that it has a multi-layer structure and may be made up of guanine crystals. At that time, however, people did not know the specific microstructure, because electron microscopy at that time was easy to destroy these structurally fragile samples.

and now we finally have a chance to see the true face of this mirror. Recently, using a frozen scanning electron microscope, researchers photographed the microstructure of the mirror surface of scallop eyes:

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this is a mosaic mirror, as previously speculated, its main body is a neatly arranged square guanine crystal. The whole mirror contains 20 to 30 layers of crystal structure, filled with thin cytoplasm. Between these multi-layered structures, the reflected light interferes, which makes the mirror best at reflecting blue-green light, which is consistent with the light environment of the scallop. The structure of these crystal sheets is very neat, which indicates that scallop controls the growth and arrangement of crystals very well, but the specific mechanism remains to be studied.

so, what is the eyesight of scallops? It may not be very good compared with humans, but the Atlantic report also mentions that researcher Daniel Speiser has conducted experiments. He showed the scallops a film of "Food particles floating". As a result, when the particles were only 1.5 mm in diameter, the scallops would open their shells and prepare to feed. This shows that their small reflective eyes are very useful.

in nature, guanine crystals do contribute to many exquisite optical structures. For example, the gloss of fish scales is related to flaky guanine crystals. People have also used this purine crystal in fish scales to make artificial pearls and pearl cosmetics. A method of blue ghostly animals has been introduced before, which also obtains dreamy structural colors through neatly arranged guanine crystals. More reading: motion picture appreciation: Blu-ray

Source:

https://www.theatlantic.com/science/archive/2017/11/scallops-have-eyes-and-each-one-builds-a-beautiful-living-mirror/547115/

http://science.sciencemag.org/content/358/6367/1172