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An enlarged view of a collector urchin’s “throwing stars.”
The wide-open jaws of these pedicellaria heads will clamp
down on whatever they come into contact with.

THE sCIENCE BEHIND THE STORY them. “You can see them with the naked eye,”

Marine ecologist Hannah Sheppard-Brennand Sheppard-Brennand said. “They look like tiny,
recently discovered the collector urchin’s shuriken- dark triangles.”
jutsu-like defense. As part of her research at Other animals shoot out defensive weapons.
Australia’s Southern Cross University, she kept Think of a porcupine’s quills or an octopus’s
collector urchins in aquariums in her laboratory. cloud of ink. But Sheppard-Brennand thinks the
Almost every time she touched the spiny animals, collector urchin is special, releasing what she calls
she ended up with pedicellaria heads stuck in the semiautonomous venomous devices in response
skin of her hands. It was more than annoying. The to a threat. In other words, when the pedicellaria
bites hurt and swelled like beestings. heads are released, they work independently from
“I wondered whether this release of pedicellaria the urchin. “The jaws of the heads open and close
heads could be in response to the risk of predation,” repeatedly, perhaps to increase the chances of
Sheppard-Brennand said. To test this hypothesis, biting a predator if they come into contact with it,”
she and her colleagues put collector urchins in she said.
small tanks. Then they gently tapped the urchins Somehow, these living “throwing stars” are
with forceps to simulate a predator attack. able to sense their surroundings, sink their fangs
Within seconds, the urchins began releasing into an attacker, and deliver a nasty bite—all on
snapping pedicellaria heads into the water around their own.

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