Under the stones, in a depth of a meter or so, Ophiuras, the brittle stars live. Some are big and smooth (only a video this time, but there are some pics from the last year), others are tiny and thorny handed.

These spikes are moveable, and ophiuras use them as little tweezers, so they can travel not only on a vertical surface, but upside down as well. Tweezers tickle and slightly prick a tenar like burdock balls.