"Identification: The Moorish Idol is not an Angelfish, nor a Butterflyfish, but rather a close relative of the Acanthruidae or Surgeonfish family. A one-of-a-kind Zanclidae family member, this fish is also often misidentified as a Pennant or Bannerfish, which are actually species of the Heniochus genus that are commonly referred to as the "False" or "Poor Man's" Moorish Idol."
http://saltaquarium.about.com/od/tan...oorishidol.htm
Tangs are Surgeonfish