coral ID
 

can anyone ID this coral. It came on a polyp rock I bought. It was really small when I got it and now it is overgrowing the rock. This is just a frag of the coral.
http://www.canreef.com/photopost/dat...nknown-med.GIF

It's a type of sponge, but,I can't remember the name. I've got a bunch of it in my tank and in a few other tanks I look after for people.