The phylum of the class Hexapoda is Arthropoda. Hexapoda refers to insects, which are characterized by having six legs. Arthropods are a diverse group of invertebrates with jointed limbs and a hard exoskeleton.

Yes.

Hexapoda (I may be wrong though).

Hexapoda is the scientific name for a group of animals that's mainly insects (Insecta) but also a few others such as springtails that are nearly insects but not quite. Hexa = six, poda = legs!

No. Insects are the the subphylum hexapoda and millipedes are in myriapoda.