elevated as orders. Scales are not present in the first instar in either order, appearing after one or more molts--two in Archaeognatha. The extent of scaling varies between taxa, with at least the three terminal filaments, tergites and abdominal coxites bearing scales in known Archaeognatha. Certain families of Zygentoma are scaleless.

Structure

The structure of scales differs between the two orders; Zygentoma scales have a membrane with raised ribs on their upper surface, while Archaeognatha scales contain a porous lumen

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