The Platycephalidae are a family of marine fish, most commonly referred to as flatheads. They are relatives of the popular lionfish, belonging to the order Scorpaeniformes. Taxonomy Platycephalidae was first proposed as a family in 1839 by the English naturalist William John Swainson. The 5th edition of Fishes of the World classifies this family within the suborder Platycephaloidei in the order Scorpaeniformes. Other authorities differ and do not consider the Scorpaeniformes to be a valid order because the Perciformes is not monophyletic without the taxa within the Scorpaeniformes being included within it. These authorities consider the Platycephalidae to belong to the suborder Platycephaloidei, along with the families Bembridae, Parabembridae, Hoplichthyidae and Plectrogeniidae within the Perciformes. Genera Platycephalidae has the following genera classified within it: Platycephalidae has been divided into as many as 5 subfamilies by some authors but Fishes of the World does not recognise subfamilies but does state that some authors recognise two subfamilies. The two subfamilies are Platycephalalinae, containing Elates and Platycephalus, and Onigociinae, containing the remaining genera. These two groupings are thought to have become divergent in the Eocene with the Platycephalinae being predominantly temperate and Onigociinae, being predominantly tropical. The basal Platycephalinae species are confined to southern Australia and the more derived taxa have diversified in the tropical Indo-West Pacific. The genus Sorsogona is recognised by Fishbase but, apparently, it does not include the type species, Sorsogona serrulata, as a species within it. Catalog of Fishes treats this genus as a synonym of Rogadius but classifies all the species in Ratabulus, including the type species, which it treats as a synonym of Ratabulus tuberculatus. Etymology The name of the family is derived from the Greek words platy, meaning "flat", and kephale for "head". Description Platycephalids are small to medium-sized fish. Most species are small, reaching an average of 10 cm in length. However, a few species in the genus Platycephalus are known to grow up to over a in length. Their most distinctive characteristic is the flattened shape of their heads. While the rest of their bodies is shaped similarly to other fish that inhabit the areas they frequent, their heads are triangle-shaped and dorsoventrally depressed, giving them the shape of a trowel or an artist's spatula. Their eyes are situated on the upper surface, in accordance with their bottom-dwelling lifestyle. They possess two complete dorsal fins, the first one supported by six to 9 strong