I bought a wild colony acropora from my LFS the other day. I thought I had dipped it and gone threw it carefully to not get any unwanted pest in my reef. Last night I saw this weird this under the rock the colony came on. Can someone please tell me what this is? If its bad or good? I tryied to pick it out using tweezers but with no success. Its rock hard, brown in color and seems to have a mouth or two.