Sea Urchin

http://en.wikipedia.org/wiki/Sea_urchin

            The sea urchin, as stated on the above link, is related to the crinoids, which are the subject of some previous posts on this site, along with images of the crinoids.                It has been speculated that the entire body of the sea urchin is one big eye.
              It has also been theorized that the crinoids evolved an ability to up their moorings and walk along the sea floor, in order to avoid being nibbled by sea urchins.   Broken off bits of crinoid stem found scattered around are evidence of sea urchin snacking.
                Sea urchins are sometimes considered a pest but are alright where they are a natural part of the ecosystem if kept under control by other predators, such as otters, which like to eat them.