How does the gula differ between homopterans and heteropterans?

The gula serves as a key anatomical distinction between heteropterans and homopterans within the order Hemiptera:

• Heteroptera: The gula is a well-developed, hard bridge that physically separates the mouthparts from the prothorax.1
• Homoptera: The gula is either small and membranous or entirely absent. This reduction allows the base of the mouthparts to abut or even fuse directly to the prothorax.1

This structural difference represents a significant functional specialization. In some homopteran families, such as those within the suborder Sternorrhyncha, the mouthparts have fused so completely to the prothorax that they remain attached to it even if the cranium is removed. The reduction and loss of the gula in homopterans, alongside the migration of the mouthparts toward the prothorax, are considered major evolutionary changes that help differentiate the phylogenetic lines of these two groups.1