Researchers studying sea urchins have found out that this marine invertebrate can use its entire body from the ‘feet’ to the tip of its spines as eyes. The findings have been published in the journal Proceedings of the National Academy of Sciences.
Earlier scientist had known that marine invertebrates respond to light, without having any eye like structure. The genetic analysis of the species done previously had also revealed that they possess a large number of genes like that of the retina, which is the light sensitive tissue present in the eyes, but again there is no specific eye like organ.
The combination of previous results lead the scientists to conclude that the retina –like genes in sea urchins is not confined at one place, but scattered all over the body on the skin which function like the retina.
The study was done on the California purple sea urchins. Previously scientists had theorized that the species spines simulated the light-blocking pigmented cells found in most animals’ eyes. These helped in blocking light from the back and sides so that the retina in the front could be used to see just like eyes.
But the recent research shows that the purple sea urchin possesses two distinct groups of bristly, light-receptor cells concentrated at the bases and tips of its 1,400-plus tube feet. Therefore, they now feel that the urchins use the tube feet as retinas and the rest of the body to shield against the extra incoming light.
Researcher Maria Ina Arnone, a developmental biologist at Anton Dohrn Zoological Station in Naples, Italy said, “Prior studies did find the number and placement of spines on a sea urchin could affect how sharp its vision might be, and this new find “might well be part of the picture.”
The puzzle to the ‘sight’ of the sea urchins is thus slowly getting revealed.