The Potential Value of the Mid-Abdominal Musculature and Nervous System in the Reconstruction of Interordinal Relationships in Lower Neoptera

The mid-abdominal musculature and its innervation are compared for several lower neopteran “orders”; data on Embioptera and Mantophasmatodea are presented for the fi rst time. For the sclerotisations, the musculature, and the nervous system of the mid-abdomen general descriptions are given, and general aspects of homologisation in these elements are explained; for the lateral muscles the distinction of three groups innervated by the T-, B-, or C-nerves is confi rmed. Differences in the musculature and nervous system of the lower neopteran lineages are discussed and evaluated with regard to their phylogenetic implications. Conditions in Ephemeroptera, Megaloptera, and Zygentoma are partly included in the discussion. Several characters were found to be informative on interordinal relationships. Plecoptera have features probably plesiomorphic at the neopteran level: the origin of nerve A in front of the ganglion and the innervation of intrasegmental lateral muscles by nerve A; this may support the monophyly of a taxon comprising all other Neoptera. The hyperneural muscle found in many Dictyoptera also appears as a uniquely plesiomorphic structure (at the pterygotan level). The co-occurrence of two specifi c lateral muscles supplied by nerve B as well as certain subdivisions in the lateral muscles may support a clade Phasmatodea + Embioptera. We also point to character systems that appear informative on the internal phylogeny of order-level taxa, such as the relationships between nerves T and M in Plecoptera, the ventral musculature in Ensifera, the dorsal musculature in Dermaptera, and details of the hyperneural muscle in Dictyoptera. Besides the very low number of taxa studied so far, major problems still persistent in the use of mid-abdominal characters for phylogenetic work are (1) the insuffi cient knowledge on topographic homologies for the lateral cuticular areas of the mid-abdomen; (2) lacking knowledge on the neuronal structural level of the mid-abdominal nervous system; (3) diffi culties in the homologisation of muscles and nerves between Pterygota and the apterygote Archaeognatha and Zygentoma, which are partly due to the presence of a system of non-cuticular tendons in the latter and limit outgroup comparison for Pterygota.