Heniochus acuminatus, commonly known as the Pennant coralfish, is a large butterflyfish, which are also sometimes refferd to as bannerfish. Their base colour is pure-white with two broad vertical black bands and a small black stripe from the forehead to the eye. The pelvic fins are black and their caudal, dorsal and pectoral fins are yellow. The dorsal fin has a very long white filament, which waves in the flow like a banner in the wind. H. acuminatus looks very similar to H. diphreutes. There are a few small differences though. The mouth of H. dipheutes is a little bit smaller (best viewed compared to the eye) and has a more robust belly/chest. And it has a more rounded anal fin where the black ends up higher, compared to acuminatus, where the black ends in the tip of the fin. H. diphreutes is also sometimes said to be more reef safe, although both are a risk in a reef tank.