What is this thing?

Hi guys. I'm not really sure where to put this as I have no idea what it is so im sorry if its in the wrong forum :(







It started out tiny and was attached to one of the liverocks we bought right at the start of our hobby so whatever it is, its hardy as hell. It has grown (a substantial amount) and multiplied. Theres even one on my heater. Now I'm quite happy to leave them be unless someone can advise me otherwise. They dont seem to be doing any harm to anything. Its very difficult getting pics. I can try and get more once my phone is charged.