What body features help scientists classify apterygotes?

Scientists classify apterygotes—a group of primitive, wingless hexapods—by examining several key morphological features that distinguish them from winged insects (pterygotes) and help differentiate between various apterygote orders.12

Primary body features used for classification include:

• Mouthparts: A fundamental criterion is whether the mouthparts are entognathous (retracted within the head, as in Protura, Collembola, and Diplura) or ectognathous (exposed, as in Zygentoma, Archaeognatha, and the extinct Monura).2
• Thorax and Legs: Scientists analyze the structure of the thorax and the specific segmentation and specialization of the six legs.12
• Abdomen: Classification relies on the number of abdominal segments, the presence and modification of abdominal appendages, and the nature of external genitalia.23
• Sensory Organs: The presence, number of segments, and structure of antennae, as well as the placement and type of eyes (simple or compound), are also used as diagnostic features.2

Additionally, scientists consider developmental traits, such as the type of metamorphosis and, in the case of proturans, the process of anamorphic growth where body segments are added during molting.23