STUDY ON THE SYSTEMATIC POSITION OF SYSTOLOSOMA BREVE SOLIER (ADEPHAGA, TRACHYPACHIDAE) BASED ON CHARACTERS OF THE THORAX

Internal and external thoracic features of Systolosoma breve Solier we re examined and interpreted phylogenetically. The irregular pattern of the elytra is considered as an autapomorphy of Systolosoma. The round ed apex of the prosternal process, the elongated, cranial part of the metasternal process which is rigidly interlocked with the deeply excav ated, separate posterior part of the meso ''sternal'' hexagonal groove , the tendency towards reduction of flight muscles, and the absence of M. dorsoventralis secundus and M. sterno-episternalis are possible sy napomorphies of Trachypachus Motschulsky and Systolosoma Solier. Parti al reduction of the metasternal transverse ridge and fusion of the mes al metacoxal walls are considered synapomorphies of Tracypachus + Syst olosoma + Dytiscoidea. This phylogenetic interpretation would imply th at the subcubital setal binding patch is secondarily absent from adult s of Systolosoma. The condition of the mesepimeron and metepimeron is in agreement with the presumptive groundplan condition of Adephaga.