Interesting comments. It's worth noting that the diet of Astropecten polycanthus is pretty much unknown, but is thought to be mainly small molluscs, possibly worms etc
Nearly everything published about this species (and all references to detritus consumption) seem to come from the aquarium hobby suppliers, which is not the best source of data. Scientific study about the feeding habits are extremely difficult to find.
Unfortunately we really don't know what they feed on or how they survive in a marine aquarium. However, they seem to only do well in very mature systems with good sandbeds and healthy invert populations.
Sadly, I think the OP's specimen has either ventured into a powerhead (unlikely given location of wound) or more likely is dying. The peppermint will be after the decaying flesh.
