What is the difference between the surgeon fish and a tang?

The fish families including the naso, acanthurus, paracanthurus and more all have a weapon either side of their peduncle  

Surgeon fish have a blunt head style like the clown and blue surgeon fishes and are omnivores.
Surgeon fishes weapon, the razor blade like weapon cuts like a surgeons scalpel.


Tangs have a pointy face, as an example, like the scopaz and are all herbivores though many adapt to being omnivores.  
Tangs weapon, though many have just one spike unlike this naso, this weapon rips the flesh.