bad star... they multiply rapidly my splitting. ive been removed around 50 or so over the last 4 or 5 yrs.i remove all that i can see (usually around 5)every month .but always one escapes detection. for the most part they are seen eating algae on tank and rocks.but i have seen them eating zoas on occassion probably when hungry.so im not to aggressive about removing them but if i see the near any zoas then they definitely get the boot.there is some info at garf.com about predatory stars
I have read that astrina(sp?) are fine to have in your tank unless you see the color "red" on them and then they are trouble, but 90% of astrina stars are harmless. I wish I could remember where I read this but can't.