Brittlestars and serpent stars are the same thing. There is no biological distinction between the two. It is made in the trade only.
"Brittlestars" have arm spines perpendicular to the arm:
"Serpentstars" have arm spines that are adpressed (parallel) to the arm:
There is no significance to this distinction, and it can be confusing.
Green brittlestars
Ophiarachna incrassata are
known predators in the wild. They do not belong in tanks if people aren't willing to risk anything. No animal is reef safe. Corals can kill corals. I believe that most people who have these animals do not have any problem with them. It is a personality issue. If they can catch food and grow, why not? That is the whole purpose of life. Grow, get big, reproduce. They aren't doing anything surprising. And when locked up in an all you can eat buffet, wouldn't you grab a few tasty bits instead of the same old stuff all the time? The golden rule is that they are not scavengers. They must be kept very well fed, and even this may not stop them. Such an animal is not simply surviving, it is thriving. The goal in nature is to thrive and reproduce. Some animals do that very well.
Having said that, I keep 5 brittlestars (inculding a green) in a 15g and have had no problems with them eating anything that I notice anyway. Feeding time is tricky because they grab food from each other, but I have not seen any other problems with them. I suspect that many people have no problems at all. Keep an eye on things. If you want, trade it back in.
Whatever behavior you see, keep in mind that we may not be aware of their potential for predation. Much of this behavior can not be observed in the wild. Also remember that these animals do not have anything remotely approaching a 'brain' by our definition.
Other brittlestars and serpentstars do not appear to have the same reputation, though there are individuals who have caused trouble. It is not easy to condemn or praise the lot.
