I don't know but I had the same thing come in as a hitchiker
the first time I saw it it was smaller then a popcorn seed, now it is as big as 50 cent piece,,and it has been 7 months
I "HAD" a pencil urchin and I hated it. I kept having to knock it off my feather duster every other day. Went skiing and my there were feathers all around my tank.. RIP.. Neadless to say I dont have him anymore..
i love mine. I think i got good coraline growth. And have heard somewhere that they can kind of help spread it. when the munch on it. I have not seen any damage yet from him and he's getting pretty big about 1 1/2 old.
Did scare me a little when he would go over to the bubble coral. Thought he was going to pop it