This could be it.
http://www.reefs.org/hhfaq/pages/mai.../faq_rock3.htm
"It is possible that this particular urchin is Echinometra mathaei which is a common hitchhiker on Indo-Pacific rock. Other Indo-Pacific hitchiking urchins may include Pseudoboletia, Tripneustes, Paraselinia, and Echinothrix species. Echinometra mathaei bore holes into rock while using its spines to hide itself. It is an effective algal grazer but can irritating to other tank inhabitants with its burrowing habits. "
I think most of my livestock comes from Indo Pacific so this could have hitchhiked in as an urchin larvae or baby urchin, and after all these years, it finally showed itself.
http://www.jaytorborg.com/Underwater...ge38%20500.jpg
http://digilander.libero.it/scubabob...s/urchin07.JPG
