they can do minor damage to soft coral occusionally. However, the damage can sometimes kill the coral, so it is best, IMO, to leave it out of the reef tank if possible.
I love mythrax and their aquarium behavior. There is a small chance it could mess with soft corals, but that could be applied to virtually all inhabitants. I don't see any reason not to have one in your reef, providing it has algae to feed off...
And just because it doesn't mean it will doesn't mean it wont. :mrgreen:
I had both peps and emeralds in my reef. Model citizens for a couple of years, then, at different times, they got a taste for corals. No fun. I wouldn't put them in a reef for just about any reason (although peps are easy to catch in a trap) because they are not worth the risk, and the emeralds really don't do such a great job as a janitor. Peps go nuts at feeding time and eat right off your corals.
They are both oppurtunistic carnivores and will eat stuff you don't want them to eat given the chance. Why take the risk?
I`ll tell you what I won`t put in another tank are hermit crabs.They crawl all over your corals and if you try to propogate one they are pulling tooth picks out or pulling your coral pieces off the live rock.Pains in the backside.