Which apterygote groups have entognathous mouthparts?

Within the group of primitive hexapods often referred to as apterygotes, the groups that possess entognathous mouthparts—meaning their mouthparts are retracted or sunk below the surface of the head—are the following:

• Protura21
• Collembola (springtails)21
• Diplura21

While these three groups were traditionally included in the subclass Apterygota, many modern specialists now classify them as independent classes separate from the class Insecta, which contains the ectognathous (exposed mouthparts) groups such as the Zygentoma and Archaeognatha.2314