The morphology of the metathorax of brachyceran Diptera is examined, particularly the metapleuron in the superfamily Syrphoidea comprising two families Syrphidae and Pipunculidae. The homologies of the metepisternum (EPS) and metepimeron (EPM) are redefined based on the metapleural suture (PlS), which bears an internal apophysis. A new interpretation of the metathorax is provided for Syrphidae. Members of Schizophora and Pipunculidae have an articulation between EPM and the first abdominal tergite in common and the (metapleural-abdominal) articulation is indicated as a synapomorphy for them. In some species of Syrphidae the well-developed metapostnotum is articulated with the first abdominal tergite and the (metapostnotal-abdominal) articulation is diagnostic of a subgroup of the family. The articulations are evaluated and discussed with respect to abdominal flexion of Diptera.
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