SEA urchins can scrape their way through rock to make their homes. This ability has long been suspected but never demonstrated, until now.
Michael Russell at Villanova University in Pennsylvania and his colleagues studied purple sea urchins from the west coast of North America. These animals attach themselves to rock, and prefer to do so in pits and holes.
In the lab, the researchers placed single sea urchins on pieces of soft mudstone, hard sandstone and tough granite. After a year, they checked the weights of the rocks, how the surfaces looked and the amount of erosion.