New morphological characters for identifying individual specimens of Haemonchus spp. (Nematoda: Trichostrongyloidea) and a key to species in ruminants of North America.

The large stomach worms Haemonchus contortus, Haemonchus placei, and Haemonchus similis are important pathogens of cattle and sheep. This paper describes characteristics of surface cuticular ridges (synlophe), which for the first time provide morphological criteria for identifying individual adult specimens of either sex. The diagnostic patterns of the synlophe on the anterior half of specimens can be observed at 400x in temporary mounts on glass slides. The synlophe can be studied in cleared preserved specimens or in living or freshly thawed frozen specimens 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. placei and H. similis. The 4 extra ridges of H. placei and H. similis are consistently located bilaterally to the 3 ventralmost and the 3 dorsalmost ridges. The 4 extra ridges of H. similis extend to the end of the synlophe posterior to midbody, but in H. placei they extend posteriorly 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 and cattle using characteristics of spicules, female reproductive system, female tail, and the synlophe.