It seems from my experiance that the stars that are white and with irregular arms are "safe". The ones that have color (grey, green,red ,brown motteling) and 5-6 distinct arms are not safe. These are ones I have pulled off perfectly healthy zoas and have found a hole in the stalk of the zoa under the star. Now I would think these are differant forms of asterina but they could just pic up colors from the zoas like nudies do. But in most cases the white irregular ones seem safe.