The big ones I had ate zoas and trees. The tiny pure white ones just seemed to like coraline. I had a severe infestation of them and got a harlequin shrimp to kill them. Sounds like you havent got that many so I would go with manual removal as you see them. Some people have them in their tanks...
I had some dime sized asterinas that attacked softies. That one doesnt look the same as the ones I had though. I'll dig up some pics in a little bit. Maybe the 3 legged one is a different one. But they can drop off body parts that regenerate into new stars
heres the best pic i could find of mine. it's retracted but you can see the tube structure and the tips of the red duster. when fully open it was layed out flat and as big as a pencil eraser.
Just reread your post...didnt notice the red part lol. Do they have white curly tubes like a big spirorbid with a red skirt? If so....wouldnt worry. Harmless.
Pretty cool! I read somewhere that they will reproduce untill their food supply run out then they turn on each other and population goes back to almost nonexistant. Mine liked to hang out under the maxi minis.
Your first water change and all your corals are colsed up? I must have missed something. How long has this tank been set up and what do you have for livestock?