When under attack, the collector sea urchin has the ability to release hundreds of miniature independent ‘jaws with teeth’ that can latch on to predators and release venom.
The discovery by Southern Cross University marine biologist and PhD candidate Hannah Sheppard-Brennand and her research team, shows sea urchins defend themselves by counter-attacking with the ‘pedicellariae’ – a personal army of venomous jaws.
Describing one of the strangest defence structures in nature, Ms Sheppard-Brennand said the function not only acts as a defence against being eaten but also as a deterrent.
Pedicellariae are semi-autonomous structures that detach from the body into the surrounding water, where they act as a cue to prevent further attack after initial contact by any overly-curious potential predators.
“When harassed, these urchins released pedicellariae into the water, producing a pursuit-deterrent halo around the urchin,” Ms Sheppard-Brennand said.
“They resemble something out of a miniature horror movie.”
The collector sea urchins live on the seafloor in tropical reefs of the Indo-Pacific, eating algae and seaweed, but have been documented moving into cooler subtropical waters.
Supervisor and co-researcher Associate Professor Symon Dworjanyn, from the University’s National Marine Science Centre in Coffs Harbour, said this surprising discovery might explain why this sea urchin was often seen out in the open while other species tended to hide in crevices or are nocturnal.
“For other sea urchin species where regeneration has been studied it can take between 40 and 50 days to re-grow these biting appendages on their shells,” he said.
“Individual urchins are capable of releasing hundreds of pedicellariae within 30 seconds; however in this study they released tens at a time”.
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