Which physical feature gives scorpaeniform fishes the name mail-cheeked fishes?

Scorpaeniform fishes are commonly referred to as "mail-cheeked" fishes because they possess a distinctive bony plate or bar that runs across each cheek.1

This diagnostic feature is formed by an extension of the second infraorbital bone, which unites with the preopercular bone to create a rigid stay beneath the eye. In many species, this structure becomes externally prominent, sometimes bearing spines or protrusions, or expanding to fuse with other cranial bones to form a protective, armor-like covering on the sides of the head.234