Toadstool Algae, Cladophora prolifera, is a hardy, shallow water alga that is suitable for refugiums or reef tanks  The name is something we made up years ago and many of the collectors in the Keys use it, but many also call these "moss balls" or "sea hair."  Each ball will be about the size of a tangerine or small orange, and will often have a whole host of little bugs and starfish hiding inside it, all of which would be great additions to a refugium.  If conditions are right, the clump will grow onto the substrate and begin to spread out.