Spiracle structure in scolopendromorph centipedes (Chilopoda: Scolopendromorpha) and its contribution to phylogenetics

The spiracles of scolopendromorph centipedes have long been a source of systematic characters based on their segmental distribution and gross morphology, but microscopic investigations to date have documented only a small number of species. A scanning electron microscopic survey of 34 species that samples the major groups of Scolopendromorpha reveals variability in such features as the structure of the peritremal margin, specific kinds of sensilla and glandular pores on the peritrema, projections on the valves that subdivide the atrium (in Scolopendrinae), and the form of the trichomes around the tracheal openings. Adding new characters from the spiracles to recent morphological datasets for phylogenetic inference reinforces the monophyly of major groups of Scolopendridae and is particularly informative for relationships within Scolopendrini. A bowl-like atrium with the tracheae opening between humps in its floor is more widespread in Scolopendromorpha than previously reported. Shared presence of spiracle muscles in Cryptopidae and Scolopendrinae may reflect convergent evolution of a subatrial cavity in these groups rather than being an apomorphic character for Scolopendromorpha as a whole.