Main Content
Closeup of a Strongylocentrotus purpuratus sea urchin.
Photograph courtesy Sonke Johnsen, Duke University
A Strongylocentrotus purpuratus sea urchin. Photograph courtesy Sonke Johnsen, Duke University
Published February 5, 2010
The spiky body of a sea urchin acts as one big, spine-covered eye, confirms a new study that tested how well urchins can see.
Sea urchins, like their close relatives the sea stars (starfish), don't technically have eyes. Instead, the ball-like invertebrates detect light striking their spines and compare the beams intensities to get a sense of their surroundings.
(Related: "Sea Urchin Genome Reveals Striking Similarities to Humans.")
To explore urchins' visual capabilities, Sonke Johnsen and colleagues at Duke University collected 20 Strongylocentrotus purpuratus sea urchins from the wild and tested their reactions to sets of black disks.
Each urchin was placed in an otherwise empty, well-lighted tank and presented with two disk sizes, first a disk 2.3 inches (6 centimeters) wide and then one 3.9 inches (10 centimeters) wide. Each disk was placed 20 inches (half a meter) away from the urchin.
"The urchins were really fussy to deal with. Some just wouldn't move, like deer in headlights … if you can imagine a deer as a spiked ball," Johnsen said.
"But I guess for them it was a bit like being in a Twilight Zone episode, just being stuck in a featureless, well-lit room."
Urchins Watch Out for You?
All the sea urchins seemed oblivious to the smaller disks, Johnsen's team found. But when the creatures were presented with the larger disks, some urchins fled while others moved closer.
Johnsen and his team don't know why the urchins reacted differently to the larger disks, although the researchers speculate that the herbivorous urchins were unsure whether the black spots signaled predator or food.
(Related: "Noisy Eaters Are Cause of Mysterious Ocean Sounds.")
But the behavior suggests that even densely spined species such as S. purpuratus have limits to their visual ranges, the study authors say. Later experiments with other species could reveal the role spine density plays in how well urchins can see.
The finding also suggests that, even though urchins don't have eyes, their visual abilities are similar to those of marine invertebrates that do have eyes, such as the nautilus and the horseshoe crab.
Latest News
Most Popular News
-
Lizard Evolving for Live Birth
A skink species lays eggs on coasts but births babies in mountains, giving a glimpse of how placentas evolved, scientists say.
-
Sharp New Titanic Wreck Pictures
On the 25th anniversary of Titanic's rediscovery, high-resolution images from a new expedition shed light on the shipwreck.
-
Photos: "Stunning" Sea Creatures
A hitchhiking anemone, a perching sea robin, and a many-armed sea star were recently spotted off the Indonesian island of Sulawesi.
Advertisement
News Blogs
-
Blog: Tiny Shrimp in Drinking Water
Rumors abound about tiny crustaceans living in NY drinking water, and at their base, they're actually true.
-
BPA, Testosterone Linked
BPA is in CDs, water bottles, even eyeglasses and now it's in your urine, too. And it may be messing with your hormones, according to new research.
-
LHC Black Hole Suit Dropped
Court decision states "the alleged injury, destruction of the earth, is in no way attributable to the U.S. government's failure to draft an environmental impact statement."
Popular on Facebook
Gulf Oil Spill News and Pictures
-
"Firecane" Myth Busted
Flaming, oily hurricanes and "black rain" are no danger to Gulf residents on Katrina's fifth anniversary—or to anyone, anywhere, experts say.
-
22-Mile Oil Plume Found
A giant plume from the Gulf spill has been confirmed deep in the ocean—and it may stick around, a new study says.
Special Ad Section
-
Vote Now
Over 14,000 photographs were submitted to the contest. Vote for your favorite finalists!
-
Watch Video
Watch Casey Anderson with his lovable best friend Brutus, the 800-pound brown bear that he raised from birth.
