If they are brittle starts then what you should do is get a small lid, like off a food container. Put a Sinking wafer of some sort in there, or sinking hikari pellets. Pop that in your tank after lights out and then leave it for an hour or so. After this time look into your tank and see how many have collected in the dish. You will probably find bristle-worms aswell. If you dont want them then remove them.
If they are Asternia stars, they are Coral eaters. I've taken 2 of these out of my tank after luckily spotting them on the back-glass. Well worth taking out if you see them but you are unlikely to find a way of "catching" them, you just have to keep an eye out.
Ben