The pregenital abdomen of a mantid and a cockroach: Musculature and nerve topography, with comparative remarks on other neoptera (Insecta: Dictyoptera)

Abstract

Musculature and nerve topography of the middle (“typical”) abdominal segments III–VI are described for male Periplaneta (Blattaria) and Sphodromantis (Mantodea). Many additions and differences to earlier contributions are included. Segmental and individual variation are considered. Differences between Periplaneta and Sphodromantis are discussed. Characters are polarised by outgroup comparison with other Neoptera and made available for phylogenetic analysis in Dictyoptera. Some proposals for muscle and nerve terminologies are given. The musculature is very similar in the two species, but Sphodromantis lacks a hyperneural muscle. Nerve topography is also largely similar, but there are striking differences in the anastomoses between the main nerves and in the spatial relations between certain nerves and muscles. A paramedian nerve was found in Periplaneta but not in Sphodromantis. In both species, segmental and individual variation are sparse in the musculature but rather extensive in the nervous system. Apomorphies of Periplaneta are the degeneration of the anterior tergo-coxosternal muscles (still well-developed in nymphs), the loss of transverse striation in the median external ventral muscles (still present in nymphs), and the presence of an anastomosis between the two major branches of the ventral nerve. Apomorphies of Sphodromantis are the loss of the hyperneural muscle, the loss of the anastomosis between ventral and transverse nerve, the presence of an anastomosis between dorsal and ventral nerve, and possibly the loss of the paramedian nerve. Some of the discussed characters could be useful in the phylogenetic analysis of the Dictyoptera, also regarding the position of the Isoptera.