Ok, I have what appears to be a Echinometra mathaei Aka Rock Boring Urchin.
I've had him for at least 2 years now but he's out growing my reef. He is about 3.5" to 4" in diameter. (spines and all) .. this is an estimate since he is only out at night its hard to tell. Anyways... great guy.. just too big for my 50gal..
Eats coraline from what I have noticed.. also never actualy seen him make a hole, just sits in the rocks wherever..
Only comes out at night.
Looking for 20$ or trade for SPS frag.