Sea Urchin Body Is One Big Eye

Prickly critters may use their feet as retinas, study says.

Sea urchins may use the entire surfaces of their bodies—from the ends of their "feet" to the tips of their spines—as huge eyes.

Scientists had already known the marine invertebrates react to light without any obvious eye-like structures—raising the question of how the animals see.

(Also read: "Eyes Made of Rock Really Can See, Study Says.")

Previous genetic analysis of the California purple sea urchin had revealed that the animals possess a large number of genes linked with the development of the retina—the light-sensitive tissue lining the inner eyeball in people and other vertebrates.

This and other research suggested that sea urchin vision might rely on light-receptor cells randomly scattered across their skin, which collectively function like retinas.

Scientists had theorized the animals' spines simulate the light-blocking pigmented cells found in most animals' eyes. Because light-receptor cells in the retina can soak up light from every direction, pigmented cells work to block light from the back and the sides so animals can "see" what's in front of them.

Now, however, the scientists have found two distinct groups of bristly, light-receptor cells concentrated at the bases and tips of the purple sea urchin's 1,400-plus tube feet. These long, suction-tipped tubes, located on the undersides of sea urchin bodies, help the organisms move.

The team suspects that sea urchins use their tube feet as retinas and the rest of their bodies to shield against the extra incoming light, said researcher Maria Ina Arnone, a developmental biologist at Anton Dohrn Zoological Station in Naples, Italy.

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," Arnone added.

The sea urchin-eye study appeared May 2 in the journal Proceedings of the National Academy of Sciences.

Read This Next

Can science help personalize your diet?
Hogs are running wild in the U.S.—and spreading disease
Salman Rushdie on the timeless beauty of the Taj Mahal

Go Further

Subscriber Exclusive Content

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet