What features distinguish adult Neuroptera from Megaloptera and Raphidiodea?

Adults of the order Neuroptera (lacewings) are distinguished from the related orders Megaloptera (alderflies and dobsonflies) and Raphidiodea (snakeflies) primarily by their head orientation and mouthpart structure.12

Key distinguishing features include:

• Head Orientation: Neuropterans typically possess a hypognathous head, meaning their mouthparts are directed ventrally (downward). In contrast, both Megaloptera and Raphidiodea have prognathous heads, with mouthparts directed anteriorly (forward).2
• Head Shape: While the head is squarish or transverse in both Neuroptera and Megaloptera, it is distinctly elongated in Raphidiodea.2
• Mouthparts: While all three groups have biting mouthparts, the larval stages differ significantly. Neuropteran larvae possess specialized piercing-sucking jaws formed by the combination of mandibles and maxillae into a hollow tube, whereas Megaloptera and Raphidiodea larvae have standard biting mandibles.1
• Ovipositor: Unlike the other two orders, only female Raphidiodea possess a long, thin ovipositor.2

While these orders share similarities in wing structure and general body plan, these specific morphological traits serve as the primary criteria for taxonomic separation.12