An X-ray microtomographic analysis of the prothoracic skeleton structure of seven Platynotina species is presented. The investigated taxa represent different morphological types of pronotal discs. Tenebrio molitor was used as a reference model to all taxonomic considerations. The anatomical evidence gathered and analyzed in this study indicates that lateral indentations of nota, which are visible in most of the Ectateus generic group representatives, corresponds with a placement of the attachments of the pleural apophyses to the bottom of pronotal disc. Therefore, they should be defined as the apophyseal depressions. Furthermore, the main observed differences between the thoracic structure of the species with conspicuous apophyseal depressions and convex pronotal nota concerns the height of the pronotal disc and the elevation of its edges. The current investigations did not revealed any significant modifications of the endoskeletal structure between the prothoraces with or without the basal indentations. The study shows that X-ray microtomographic analysis is a powerful, non-destructive tool for the taxonomic considerations and that it can be safely applied to the name-bearing types. Furthermore, the application of this method, even to the dried entomological material, may provide many advantages over traditional morphological investigations.