NEW MORPHOLOGICAL CHARACTERS FOR IDENTIFYING INDIVIDUAL SPECIMENS OF HAEMONCHUS SPP (NEMATODA, TRICHOSTRONGYLOIDEA) AND A KEY TO SPECIES INRUMINANTS OF NORTH-AMERICA

The large stomach worms Haemonchus contortus, Haemonchus placei, and H aemonchus similis are important pathogens of cattle and sheep. This pa per describes characteristics of surface cuticular ridges (synlophe), which for the first time provide morphological criteria for identifyin g individual adult specimens of either sex. The diagnostic patterns of the synlophe on the anterior half of specimens can be observed at 400 x in temporary mounts on glass slides. The synlophe can be studied in cleared preserved specimens or in living or freshly thawed frozen spe cimens mounted in water. The synlophe of H. contortus has 30 ridges in the region of the posterior half of the esophagus, 4 fewer than H. pl acei and H. similis. The 4 extra ridges of H. placei and H. similis ar e consistently located bilaterally to the 3 ventralmost and the 3 dors almost ridges. The 4 extra ridges of H. similis extend to the end of t he synlophe posterior to midbody, but in H. placei they extend posteri orly only to the end of the anterior quarter of the nematode. A key is included to the 3 species of Haemonchus parasitic in domestic sheep a nd cattle using characteristics of spicules, female reproductive syste m, female tail, and the synlophe.