Heniochus acuminatus or diphreutes?

[Acam]

I just bought this guy from bluezooaquatics as a large Fiji bannerfish, hoping to get the reef-safe h diphreutes. Can anyone ID him? He's in QT until I can be reasonably sure he won't decimate my lps.

 

[ssavader]

This is one way to tell- diphreutes has a relatively straight chin line with only a very mild curve from the snout to the breast. Acuminatus has a pronounced s-shape curve from the snout to breast.

 

[Danieltank]

I would say acuminatus. You can tell the difference by looking at the mouth/nose

acuminatus:
http://www.liveaquaria.com/product/prod_display.cfm?c=15+25+242&pcatid=242

diphreutes:
http://www.liveaquaria.com/product/prod_display.cfm?c=15+25+3111&pcatid=3111

 

[SDguy]

The anal fin is the easiest way to tell, since it doesn't depend on the age or size of the fish:

http://www.reefcentral.com/forums/showthread.php?t=1626751&highlight=acuminatus+diphreutes

 

[nonimmigrant]

I have one each (2.5") in my QT tank. Other than what Peter points out, I've noticed that the acumulatus' pelvic fins are rounded whereas the diphreutes' are pointed. Just an observation that is very pronounced...