The class Entognatha includes three orders: Collembola (springtails), Protura (coneheads), and Diplura (two-pronged bristletails). These small, wingless arthropods are characterized by their internal mouthparts and segmented bodies.

For the purpose of life history, the insects maybe divided into three groups, the Ametabola, the Hemimetabola and the Holometabola. The Ametabola This division includes four orders of small wingless insects: the Diplura, the Thysanura, the Collembola, and the Protura. The young hatch from the egg with the adult form of body; they differ from the adult only in their size and their sexual immaturity

There are not five clean cut classes of arthropoda. There are three classes under the subphylum Chelicerata, which are: Pycnogonida, Merostomata, and Arachnida. Then under the subphylum Mandibulata, there are three superclasses: Myriapoda, Crustacea, and Hexapoda. Myriapoda has four classes: Chilopoda, Diplopoda, Pauropoda, and Symphyla. Crustacea have six classes: Ostracoda, Maxillopoda, Remipedia, Cephalocarida, Branchiopoda, and Malacostraca. The Hexapoda superclass has four classes: Collembola, Protura, Diplura, and Insecta.

The Hexapoda subphylum has a couple classes, Insecta with all the insects, and Class Entognatha, which have mouthparts retracted into the head; below which are significantly smaller wingless groups: Collembola, Protura, and Diplura. Some of these groups were formerly classified under Insecta.

Partly based on recent research, there is still debate about classes under hexapoda, some models will show up to four sub groups including those of uncertain classification.

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