Scallops: Not just extraordinary in taste but in vision too

Most of us know scallops for being a tasty dish to order in a restaurant, and maybe some of us even know that they are originally in shells.  But these underwater clams are far more interesting than we may have thought, as their extraordinary eyesight continues to amaze scientists.

Scallops: What do we know about their eyes already?

Scallops eyes have always been a point of interest for scientists.

Scallops eyesight is so good that they are in fact very similar to some of the most advanced telescopes to date, an example being NASA’s James Webb Space Telescope which is set to launch into orbit in 2019.

What does new research tell us about scallop eyes?

Over the last few days, new research has been released on scallop eyes by a team at the Weizmann Institute of Science in Israel and Lund University in Sweden.  Whilst in the past it has proved difficult to accurately analyse this part of the scallop eye, new research have found a way to get around this.

Now the crystals have been identified as guanine, scientists have further discovered their startling structure:

• The guanine takes the shape of flat, square crystals that are bunched together and layered on top of one another in curved structure.  If you grew them in a lab, the shape would be completely different, forming a chunky prism instead!
• These mirrors in a scallop eye is not a structure of the eye but a real living thing!  The square crystals grow inside the scallop eye, effectively filling them up and shaping the layers as they form
• The scallop’s mirror is slightly tilted in relation to the two retinas.  According to The Atlantic, this means that the mirror focuses light from the center of the scallop’s visual field onto the upper retina, and light from the periphery onto the lower one

How does the human eye compare to a scallop eye?

When light comes into a human eye it passes through a lens which then focusses onto the retina, which is a layer of light-sensitive cells. When light enters a scallop eye, it goes through a similar lens like structure, however it then passes not one but two retinas that are layered on top of one another, finally hitting a curved mirror at the back of the eye.  It is this mirror which then reflects and focuses the light back onto the retinas, not the lens.

Since the 1960s, scientists have known that at the back of their eyes, scallops use mirrors to reflect light forward and project images onto their double retinas.  Just like a radio telescope uses a large reflective dish to gather light to centre on a sensor, the mirror in a scallop eye focuses light on their retina.

But what has continued to stump researchers all these years is what these mirrors are made out of and how they work.  Michael Land , Professor of Neurobiology at the University of Sussex in the 1960s identified the mirror and could demonstrate how it was made up of layered crystals.  Land even predicted the crystals to be made of guanine  – one of the building blocks of DNA.  Whilst this could not be proved over fifty years ago, new research this year has shown just how accurate Land’s predictions were!

Whilst there is still further study to be done on how scallops control the formation of these crystals so finely, this is a major breakthrough.  Their vision may not be able to match ours just yet, but for a scallop I think it’s safe to say it is pretty darn impressive.

Sources

The Atlantic

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