but no spines that i can see so cant be that in the link so hmmm... I guess im going to have to bow out on this one im not to sure but it does look like an urchin and i have seen these before at the Boston aquarium
I have a donut that is the first coral I bought, back when the earth was still cooling, its been through every mistake possible and still going strong lol, they are pretty tough, hope it is a Button they are cool