They are found worldwide in diverse habitats. The first fossils are from later Carboniferous. Not included in the four groups are the extinct Phasmomimoidea and Vitimiidae, the relationships of which are unclear. In these groups ears consist of foretibial tympanae linked via modified tracheae to the enlarged mesothoracic spiracles that are modified for an auditory function. The tarsi have three to four segments.
Ensiferan mandibles are elongate and possess a prominent incisor.
The gut's proventriculus consists of a globular body lying between two bulbous gastric caeca. Classification A number of different classification schemes have been proposed. Discussion of Phylogenetic Relationships Monophyly of terminal taxa. Stenopelmatidae is, however, problematical. There is no consensus on the evolutionary history of the relationships among families.