Hexapoda

The subphylum Hexapoda, meaning "six legs", is the largest group of arthropods. It includes the insects and three much smaller groups of arthropods without wings: Collembola, Protura, and Diplura. 
All of these were once called insects. It seems they are polyphyletic, and evolved independently from each other. In other words, hexapoda is composed from the insects and the Entognatha. "Hexapods" are so called because they have a thorax with three pairs of legs. Most other arthropods have more than three pairs of legs.
Alternatively, the Hexapoda could be eliminated because they are polyphyletic, the Insecta promoted to sub-phylum, and the minor groups become "incertae sedis". This is a Latin term meaning "of uncertain placement" and used for a taxonomic group when its broader relationships are unknown or undefined.