Strange ball

I took this picture near Sharm el Sheikh and can't figure out what it is? An old sea urchin overgrown with coral and sponges?? Any ideas?

/Erik

My poor invertebrate knowledge agrees with your theory of an overgrown sea urchin... It is odd though that nothing ate the sea urchin when it died or that it didn't simply desintegrated (most sea urchins loose their spines when they die) before being overgrown. Maybe it is a live one with a living camouflage cover? Leslie?