It came out of know where

[mah0031]

Looks like Long-spine Urchin, reef safe? Must have been on the last live rock I put in a couple months ago. A freebie

 

[cloak]

It might be one of those Rock Boring Urchins. Sometimes these will hitchhike their way into our tanks on live rock.

http://www.thatpetplace.com/Echinometra-lucunter-rock-boring-urchin-216837

 

[NanaReefer]

Your rock will definitely be free of coralline algae and any other algae if available. If not they can bore into the rock cause structural issues.

 

[Waters]

It actually looks like you have two...isn't that a second one directly to the left?

 

[Chris Adams]

^^^ ya waters I think I see it to the left of the snail almost hidden just see spines

 

[mah0031]

Thanks I think your right two of them!