Which characteristics distinguish the order Osmeriformes from other protacanthopterygians?

The order Osmeriformes is distinguished from other protacanthopterygians—specifically the Salmoniformes and Esociformes—primarily by the presence of a complex posterior branchial structure known as the crumenal organ.1

While members of the superorder Protacanthopterygii share general characteristics such as the presence of epicentral cartilages and the absence of proximal forking in the intermuscular bones, the Osmeriformes are further characterized by the following:

• Anatomical features: They possess a crumenal organ, a specialized structure located in the posterior branchial region.1
• Habitat: Unlike the primarily freshwater Esociformes, Osmeriformes are found in both freshwater and marine environments across all oceans.1
• Adipose fin: While an adipose fin is present in many members of the superorder, it is a consistent feature in many forms of Osmeriformes, whereas it is notably lacking in the order Esociformes.1