The following paper argues that the primitive hexapods (Protura, Diplura,
Collembola) clade together (with other insects) in a holophyletic Hexapoda.

What is really interesting about the following

paper is that Protura and Diplura may form a clade which they call
Nonoculata.  If so, it provides further proof that Protura + Collembola do
NOT form an exclusive clade called Ellipura.  So I guess Nonoculata +
Ectognatha could clade together, while Collembola could have evolved
hexapody convergently.  So the hexapod debate continues with yet another
"twist".  Anyway, here's a link to that paper:

             Ken Kinman