Which characteristics distinguish the order Esociformes from other protacanthopterygians?

The order Esociformes—which includes pikes and mudminnows—is distinguished from other protacanthopterygians by several specific anatomical and biological characteristics.1

Unlike many other members of the superorder, the Esociformes lack an adipose fin and a mesocoracoid bone in the pectoral girdle. Furthermore, they are characterized by the following features:1

• Dentition: The maxilla is toothless.1
• Digestive System: They lack pyloric caecae.1
• Skeletal Structure: The tail is supported on three separate vertebral centra, and the snout region of the skull contains two sets of paired ethmoid bones.1
• Habitat: They are exclusively freshwater fish found in the Northern Hemisphere.1
• Swim Bladder: They possess a swim bladder with an open duct.1

These traits help differentiate them from the orders Salmoniformes and Osmeriformes, which generally retain features such as the adipose fin and different configurations of the pectoral girdle and jaw.1