Researcher Hannah Sheppard-Brennand at the coast near Coffs Harbour. Credit:Southern Cross University However these appendages, known as globiferous pedicellariae, usually remain attached to the sea creatures, which feed on algae and weed on relatively shallow ocean floors. The collector sea urchin is different. "When harassed, these urchins release pedicellariae into the water, producing a halo around the urchin," Ms Sheppard-Brennand said. "It's like something out of a miniature horror movie."

Collector sea urchins have an amazing defence mechanism, scientists have found. Credit:Southern Cross University She said that people who regularly handle these urchins report being bitten. They are a seafood delicacy in many countries, including Japan, so fishermen - and marine biologists - are particularly susceptible. The pedicellariae head of a collector sea urchin with its 'jaws' open and teeth revealed. Credit:Southern Cross University "When you're working with the animals you get a lot of pedicellariae on your hands. We've all been bitten at some stage," Ms Sheppard-Brennand said.

"When they do bite you, if feels like a bee sting or a bull-ant bite. It burns and the area swells up. You get a hive and sometimes the area can ache for 24 hours." In the ocean, she said you are more likely to be injured by the spines on the urchins when you step on them. The species in this research, which is published in the June edition of The American Naturalist, is a common tropical and sub-tropical species. "It is not often found off the coast of Sydney," Ms Sheppard-Brennand said. "But it is common in the waters further north, such as around the National Marine Science Centre at Coffs Harbour." The urchins have hundreds to thousands of these detachable jaws charged and ready to deploy.

Ms Sheppard-Brennand said they are unlikely to release them all at once. "We have observed them releasing hundreds at a time," she said. "Even then, they are in such high density - hundreds or even thousands on a single urchin - that they retain an arsenal while they are regenerating." In similar species it takes 50 to 60 days to regrow the venomous jaws. University of Sydney Professor of Marine and Developmental Biology Maria Byrne, who was not involved in the study, said collector urchins would also cover themselves with bits of shell, rubble and even plastic.



"It is thought that the cover acts as a camouflage so that fishes don't see them, but if they are hassled by a fish they have their defence in the battery of toxic pedicellaria," she said. Ms Sheppard-Brennand's supervisor is Associate Professor Symon Dworjanyn from the National Marine Science Centre in Coffs Harbour.

He said that this surprising discovery might explain why this species of sea urchin is often seen on the open sea floor while others tend to hid in rocks or are nocturnal. The urchin's venom is non-lethal even to the fish and lobsters that hunt the urchins. Rather, it helps act as a deterrent to pursuit. "When they release the cloud of pedicellariae into the water, something is released with it that acts as a deterrent to pursuit," Ms Sheppard-Brennand said. She said in conjunction with other defences this helps them to evade predators. And are they tasty?

"People in my lab have eaten them in front of me. But I feel I know too much about their life cycle - from baby to adult - so I've personally never eaten one."