I've never had a linckia, well I did once for about two days...............it melted.
So as far as diet I don't know. I have had the orange knobby in the reef (with clams) for years, and it is a detritus, algae pellet eater. And also white stars...
The new fromia has been on the rock mostly, and on the glass a couple times. So far the behavior is similar.
My orange knobby had a run in with an anemone recently however, and has that story to tell complete with pics, but I just haven't had time.
