Dictionary of Ichthyology  

beak = the structure formed from teeth which are fused in the form of a beak, e.g. incisiform teeth in Scaridae used to detach coral pieces as food; in puffers upper and lower jaw teeth have a median suture, hence Tetraodontidae

Tetraodon fahaka (= lineatus) from Boulenger's "The Fishes of the Nile". Photograph by Brian W. Coad

Canadian Museum of Nature