The little snail is an Engina species, either Engina carolinae or Engina zonalis. They are predators, but shouldn't be much of a problem in a reef tank. They will most likely eat worms and small vermetids, and maybe other tiny animals. Same family as the "Bumblebee Snails" that the suppliers all sell.
Engina carolinae Engina zonalis
Cheers,
Don