Eyes come in many sizes, shapes and structure.  Most vertebrate animals have two simple eyes.  Insects have compound eyes that allow some of them to see almost 360 degrees around them.  Spiders have 8 simple eyes.  Some fish have double lensed eyes.  A number of invertebrates have light sensitive eyespots that don’t really qualify as eyes per se.

One thing all of these have in common is the ability to sense light and dark stimuli and react to those differences.  But what about animals that can react to light and dark that don’t have eyes?  How do they accomplish this?

Sea urchins move and react to light and dark stimuli, but have no visible eyes.  Researchers from the University of Gothenburg, Sweden, have been studying them trying to find an answer to this question of how they detect the light.

Their study revealed that sea urchins have a number of genes that are involved in the production of an eye protein known as opsin and the production of light sensitive tissue.  They discovered that the light sensitive tissue forms photoreceptors at the tip and base of each of their tube feet.  These feet are located all over the sea urchin’s body, giving them the ability to detect light stimuli in all directions.

According to Sam Dupont from Gothenburg’s Department of Marine Ecology explained their conclusions by saying:

We argue that the entire adult sea urchin can act as a huge compound eye, and that the shadow that is cast by the animal’s opaque skeleton over the light-sensitive cells can give it directional vision.

As I was reading this interesting article on another unique design feature in nature, I fully expected to read something explaining the photoreceptors in the sea urchins as being some type of primitive precursor to the evolution of eyes in higher animals.  To my surprise, the only statement made which referred to evolution was:

Charles Darwin and other evolutionary biologists were bewildered by the eye’s complexity and wondered how this kind of structure could have evolved through natural selection.

Needless to say, I was quite pleased to see such a statement from a source that regularly reports on nearly every claim made by the evolutionary community.  It’s refreshing to see some honesty in reporting, even if it is just this one time.


Sea Urchins See With Their Whole Body, RedOrbit.com, July 1, 2011.

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