Discussion of Phylogenetic Relationships
The position of Diplura in the hexapods is unclear. Traditionally, it has been placed with the Collembola and Protura in a group called "Entognatha",
=== Collembola ===| ==Entognatha=| === Protura =====| | | ====== Diplura | =================== Insecta
so named because members of these three orders all have the base of the mouthparts internalized, so that the mandible and maxilla are partly contained within the head capsule. In addition to this derived similarity in mouth structure, these three orders share reduced Malpighian tubules and compound eyes. However, there is some evidence that diplurans may instead be the sister group of insects:
=== Collembola ===| | === Protura =====| | === Diplura ===| === Insecta
Derived characteristics linking diplurans with insects include the presence of filiform cerci, and an extra set of nine single tubules in the axoneme of the sperm. For a more detailed discussion of the evidence, with additional references, see Kristensen (1991).
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