I have one huge barnacle that came on some oysters that are acting as the substrate for some hairy mushrooms that I bought. The whole thing has been in captivity since November, and the barnacle is still alive (its shell is the approx. size of a grown-up's thumb, from the top joint up.) I have some small gobies and gorgs in w/ it now, and feed cyclops, cyclopeeze, and phyto.