Alignment and homology of male terminalia in Curculionoidea and other Coleoptera

Male genitalia and associated internal sclerotised plates have been long recognised in beetle taxonomy, but their relative position in the connecting membrane and the genital membrane folding patterns have never been thoroughly investigated. In this study, the structure of the genital chamber in weevils (Curculionoidea) and other Coleoptera has been investigated in detail, focusing primarily on the alignment of the 9th abdominal segment and true genital plates. Three basic types of genital alignment are recognised based on the orientation of sclerotised plates and membrane folding: (1) a primitive eucinetid type (both 9th segment and tegmen non-inverted); (2) a derived phytophagan type (both 9th segment and tegmen inverted) and (3) a cucujid type (9th segment non-inverted, tegmen inverted). A different origin is here postulated for the parameroid plate in Curculionoidea, Chrysomeloidea and a part of the Cucujoidea (from the fold of the membrane linking tergite 9 with the tegmen) and for the true parameres in the remaining Coleoptera (from the fold of the membrane linking the tegmen with the aedeagus); hence these alignment types are considered non-homologous. The superfamily Cucujoidea was found to be heterogeneous with regard to genital alignment and considered polyphyletic. The proctiger and the paraprocts of the beetles are interpreted as belonging to the 9th abdominal segment and no extrategminal plates of the 10th segment were found in Coleoptera. Arguments for and against a hypothetical homology of beetle genitalia with abdominal segments 10 and 11 are discussed.