I have the exact same thing as the upper circle but cant say forsure what it is. I know the tiny stars like to sit like that to catch food and such but would like to see rest or it before i say forsure!!
They eat extra food and crap that is in tight spots as long as they dont get out of control they are fine, I like to call them part of my clean up crew..
For sure a bristle worm, I had one in my tank that grew to 10 inchs may have been my feeding habits IMO would leave in tank as part of the unseen cleaning crew!!!!
Thank you ophiura for being level headed, this planet will take care of itself weather we like it or not, i dont watch news any more its mostly bs, but cant help to day dream a bunch of us over there trying to save some coral, just cause we care!!!
You might need body to do return/exchange, and ive had to learn the hard way seems like lfs kids and adults dont sometimes know anything about what their selling!!!