Assuming GARF's identification as
Asterina anomala was even correct, that animal was reclassified in 2004 and is now called
Aquilonastra anomala. The taxonomy of asterinids has been in revision for the past several years now based on new molecular information.
It would seem, based on anecdotal reports from hobbyists, that there are at least three or four different species (perhaps more) of asterinids that are commonly found as hitchhikers in reef aquariums. Fortunately, the great majority of them seem to be harmless substrate feeders.
In my own experience, these little starfish never caused any problems at all. In fact, I received mine as part of a package from one or more online vendors. I believe they called them "micro stars" and they called the tiny little brittle stars "mini stars." I could be wrong but I believe that's what they were called. In any event, I received some of the tiny whitish little asterinids and some of the tiny little brittle stars from the same online vendor. Both multiplied in my tank and neither caused any problems whatsoever.
According to Dr. Ron Shimek: "Occasionally, some populations of these asterinids have been reported by aquarists to eat either soft corals or stony corals. These coral-eating forms, perhaps different species, seem to be quite uncommon, constituting less than five percent of the various populations."
P.S. -- I just checked and it appears that I received both "micro stars" and "mini stars" from
Inland Aquatics and just "mini stars" from
IPSF. The little asterinids are called "micro stars." The tiny brittle stars are called "mini stars."