AFFILIATION OF HYOSTRONGYLUS-RUBIDUS (NEMATODA, TRICHOSTRONGYLIDAE) WITH THE OSTERTAGIINAE, AND EVALUATION OF THE SYNLOPHE AND OTHER STRUCTURAL CHARACTERS

Classifications of the Trichostrongylidae have referred Hyostrongylus Hall, 1921, to the Ostertagiinae or the Graphidiinae. The genital cone and synlophe of Hyostrongylus rubidus (Hassall and Stiles, 1892) were studied to clarify the subfamilial position of the genus and to asses s hypotheses for the origin of the Ostertagiinae. Paired ''O'' papilla e, a putative synapomorphy for the Ostertagiinae, are located on the v entral aspect of the genital cone in H. rubidus. This character, along with the structure of the bursa, confirmed placement of Hyostrongylus in the Ostertagiinae rather than the Graphidiinae. The synlophe was c omposed of a largely symmetrical system of continuous ridges extending from the cervical zone to near the caudal extremity in males and fema les. At the midbody there were 40-58 ridges; in females the vulval reg ion was modified by irregular cuticular inflations. It was concluded t hat current concepts for independent origins of genera of the Ostertag iinae from the Graphidiinae were not supportable, as such would result in polyphyly for the former and paraphyly for the latter subfamily. A dditionally, the genus Cervicaprastrongylus Gibbons and Khalil, 1982, was considered to be distinct from Hyostrongylus.