I still believe it is a Tunicate (sea squirt) as I said previously in your other thread. It's movements and appearence are consistant with the filter feeding action that tunicates use. It's not a worm, as all worms I know of, that are stationary have a shell or tube of some sort. It's not a medusa worm, nor is it a cucumber. There is more types of sea squirt then I can count and little is known about them so finding a litteral 100% ID on this one is nearly impossible. There is nothing to worry about.