So, I bought some new live rock to put in my tank and while it was curing I noticed this...thing on one of the rocks. It has a shaft very similiar to that of a feather duster only a bit more plate/scaley. The top of it looks like it may have been crushed by some other rocks in the bin it came from and every now and again a tentacle or two pokes out then goes back in (I dont think that it can fully extend due to the damaged opening). Is it a pest? It actually looks like a smaller version of some...thing I saw at an aquatic store today.