Why is the classification of the order Gasterosteiformes considered uncertain?

The classification of the order Gasterosteiformes remains unsettled among scientists due to ongoing debates regarding the placement of specific families and the overall grouping of these fishes.1

The uncertainty stems from several factors:

• Disputed Groupings: Some authorities argue that families such as Aulostomidae, Centriscidae, Fistulariidae, Solenostomidae, and Syngnathidae should be categorized under a separate order, Syngnathiformes.1
• Placement of Pegasids: The family Pegasidae is particularly difficult to classify. While sometimes included within Gasterosteiformes, other experts suggest grouping them with sticklebacks or pipefishes, or even assigning them to their own distinct order, Pegasiformes.1

Because these classifications rely on complex interpretations of skeletal structure, body plates, and fin positioning, a definitive consensus has not yet been reached.21