All Diplura possess the following defining characters: (1) elongate body, (2) 10th abdominal segment with a pair of caudal cerci or one segmented forcep-like pincers, (3) absence of eyes, (4) entognathous mouthparts, and (5) two pair of spiracles on the thorax (Fig. 1).

There is no doubt that these organisms are primitive arthropods standing near the base of the evolutionary lineage that led to the class Insecta. Whether they should be included in the Insecta or merit a class unto themselves is debatable. Kristensen assigned them to their own class (class and order Diplura) in 1991. This suggestion, although it may be correct, has not been followed in general textbooks of entomology. The classification within the order Diplura has developed gradually over the past 100 years as our knowledge of the group increased. Table I lists the major taxa and their general distribution.

The 1000 or so species that have thus far been described may represent only 50% or less of the actual world fauna. Distribution records of the known taxa are poor, with many species known from a single locality. A great deal of work is left to be accomplished before an accurate idea of the diversity and distribution of the Diplura is known.

FIGURE 1 Dipluran (Parajapyx sp.). (Illustration by K. A. Justus.)
TABLE I Classification of the Diplura

Class or order







Anajapygidae (1 genus Anajapyx, 4+ spp.;

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