Mail-cheeked fishes include stonefish, lionfish, and sculpins
Scorpaeniformes are a diverse order of ray-finned fishes—stonefish, lionfish, sculpins, and kin—also once called Scleroparei. With over thirteen hundred twenty species they rank among the five largest bony-fish orders. A bony “suborbital stay” braces the cheek and gives the mail-cheeked nickname.
That stay is a backward extension of the third circumorbital bone across the cheek to the preoperculum in most species. Members are carnivores eating crustaceans and smaller fish. Most hug relatively shallow bottoms, though some haunt deep water, midwater, or even fresh water. Heads are often spiny; pectoral and caudal fins tend to be rounded. Most stay under thirty centimetres, yet the order spans tiny velvetfishes to much larger forms.
Suborder Scorpaenoidei is largely benthic. Within it, sea robins split into ordinary and armored families—the armored line bearing spine-studded plates the others lack. Across the order, venomous spines and camouflage recur as themes in predators that wait more than chase.
The second branch of Scorpaenoidei, the scorpionfishes, spans twelve families according to Minouri Ishida's 1994 work and later studies, and runs from 2 or 3 centimetres up to about a metre long. How to carve the whole order into families is still unsettled, with counts ranging from 26 to 35. The fifth edition of Fishes of the World lists colourfully named groups including racehorses, also called pigfishes or horsefishes, Australian prowfishes, the red velvetfish, the cofish, and three kinds of flathead: deepwater, true and ghost.
From reef lionfish to cryptic stonefish, mail-cheeked anatomy is a shared scaffold for ambush. The cheek brace is an obscure bone with a public consequence: a huge radiation of bottom hunters built on one facial strut.
Source: Scorpaeniformes
