part of continuous with pupal spiracular tracheal branch 1 pupal spiracle anterior pupal spiracle FBbt:00002997 The only functional spiracle of the pupa. These spiracles form as evaginations of the epithelium in the prothoracic segment, first apparent in the contracted third instar, just prior to pupariation. They are biperforate and open into the space between the pupa and the hardened puparium. fly_anatomy.ontology Prothoracic segmental identity from Whitten, 1957 & 1980. Note that this is different from the segmental identity assignment of the anterior thoracic spiracle of the adult. functional pupal spiracle tracheal metamere 1