I think there are several types of Asterina stars. Most are harmless, but some have been reported to eat pocillopora and Stylophora with a passion. I'm sure ther eare some that eat zoas, too. Those look like the ones I have (many color variants in my tanks and they all 'seem' harmless so far...). Assymetry is a common trait, so if you see others with large legs and small legs, it is the same (just has divided).