Chaetodon sedentarius has the common name reef butterfly, one of the few Atlantic species. Who knows though at a LFS. Here's a pic of what it is if they have it identified correctly.
Pretty much all of the butterflies of the Chaetodon genus are hit or miss when it comes to their "safeness" in reef tanks. Depends also on what you keep in the tank. The VP of my club has had a raccoon in his tank for a while with success, but has mainly sps corals. I don't recommend you trying one unless you truly know what you're getting into and are willing to take the risk, but if you do out of this genus go for plankton feeders.
For the most "reef safe" look for those in the Hemitauricthys genus, like the pyramid or zoster butterfly. Also look into the long nosed butterflies, or Heniochus diphreutes. Before you make the decision though do some research.
Butterflies are not for the novice, and especially not for the novice reef tank.