Arrow crabs aren't interested in eating hermit crabs or snails, they can't eat them becase they are in a shell. But they will make attempts at eating peppermint shrimp, anemone and sexy shrimp and any other shrimp smaller than a peppermint.
They also try to eat small fish too, they can catch anything smaller than 2 inches. They also pick at corals and especially feather dusters and almost any kind of filter feeder. It says they are reef safe, but when they get big, they can be dangerous to corals and fish and shrimp. And I had a xenia, the arrow crab chopped off a whole stalk.
Fish4lyfe says that they won't nip at anything if they are well fed, but I fed mine atleast 3-5 times a day, adn it was always hungry, and it grew rapidly.
Arrow crabs are also very territorial with Coral Banded Shrimp, they will fight alot, especially in that sized tank.
You might be safe if you get a small one, but they grow quickly.
