I did some tank moving a few weeks ago and stirred up sand and move rocks around. Now I think these are those worms that normally build tubes in the sand (not feather dusters) out of a mucus and sand combo, but moving the tank around has them hanging out on the rockwork. They seem perfectly content on the rocks, whatever they are and appear to just gobble up any debris that is near enough for their tentacles to reach. I also see what appear to be babies that drift around to look for a new spot now and then. And I’ve got different colored ones too, some are a dull purple with white speckles, most others are more clear than anything else. Tank is 8 years strong.