Agreed, they are zoa pigs. I have really great water quality but they show up and for whatever reason like the nicer looking zoas. I just bought a harlequin shrimp last week and I have to say it is one awesome looking critter besides the fact that it chows on the starfish. Once they are gone, I'm going to toss a few chocolate chip starfish in my sump and feed one leg at a time to the harlequin. That is what was suggested to me. A little creepy but....