The male abdomen of the relic termite Mastotermes darwiniensis (Insecta : Isoptera : Mastotermitidae)

The primitive Australian termite Mastotermes darwiniensis Froggatt, 1896, i s crucial for phylogenetic analysis in Dictyoptera. Its posterior male abdo men from segment VI on is described here. Included are all exoskeletal comp onents and muscles, and most parts of the internal genitalia. Comparisons a nd homology discussions are given for most elements within the range of Dic tyoptera, and the polarity of characters is discussed. Spiracle muscles and internal ventral muscles IX/X are discussed in a wider systematic frame; s imilarities between insects and the chilopod Lithobius are indicated in the former muscles. In the middle as well as in the terminal abdominal segments Mastotermes lar gely corresponds with Blattaria and Mantodea. The most striking difference, however, lies in the external genitalia, which in Mastotermes are perfectl y symmetrical and reduced to a flexible papilla with weak ventral sclerites . Coxosternum IX (subgenital plate) in Mastotermes is designed as in other Dictyoptera but lacks anterior apophyses. The spiracle closing device is li ke in Blattaria and Mantodea; a manubrio-paratergal dilator muscle is proba bly peculiar to Dictyoptera. The basal parts of the tracheae, next to the s piracle orifice, have a sculpture of anastomosing ridges present also in Pe riplaneta. The median external ventral muscles are, as in Periplaneta but i n contrast to Sphodromantis, non-striated. The hyperneural muscle along the abdominal nerve cord resembles that of Periplaneta; it has been lost in Ma ntodea. Abdominal characters promising for phylogenetic analysis of Dictyop tera are surveyed, and an update is given of current evidence on the phylog enetic position of the Isoptera. Character evaluation, however, remains inc omplete due to the lack of morphological data for comparison.