Cidaroid urchin with serrated arms that look somewhat like edge of steak knife.
Wonder if these would cut someone handling them? Note that what appear to be
younger, perhaps regenerated spines are smooth on edges.
Image ID: expl5534, Voyage To Inner Space - Exploring the Seas With NOAA Collect Photo Date: 2010 July 28 Credit: NOAA Okeanos Explorer Program, INDEX-SATAL 2010