title: Scanning electron microscopy of the sheathed infective larva and parasitic third-stage larva of Haemonchus contortus (Nematoda: Trichostrongyloidea).
abstract: Scanning electron microscopy was used to describe the infective and parasitic third-stage larvae of Haemonchus contortus, the large stomach worm of ruminants. Infective larvae are ensheathed in the cuticle of the second stage, so the descriptions are of the second- and third-stage cuticles. Both larval stages had an inner circle of 6 labial papillae, an outer circle of 6 labial papillae and 4 somatic papillae, and lateral amphidial pits. Infective larvae (cuticle of the second stage) had the 6 internal labial papillae on prominent bluntly rectangular lappets in a star-shaped arrangement around a large triradiate mouth, small triangular or round amphidial pits, flattened ribbonlike lateral alae, and phasmidial apertures opening on the ventral surface of the lateral alae. Parasitic third-stage larvae had the 6 internal labial papillae on small elevations without lappets around a small mouth; large, oval amphidial pits; ribbonlike lateral alae for most of their length, but with the anterior 30-40 microns of the alae cordlike; and phasmidial apertures on the body cuticle ventral to the lateral alae.
authors.affiliation: United States Department of Agriculture, Livestock and Poultry Sciences, Institute, Beltsville, Maryland 20705.
authors.forename: J R
authors.initials: JR
authors.lastname: Lichtenfels
authors.forename: H R
authors.initials: HR
authors.lastname: Gamble
authors.forename: J P
authors.initials: JP
authors.lastname: Purcell
mesh_terms: D000818:Animals; D006189:Haemonchus / Q000648:ultrastructure*; D007814:Larva / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D012756:Sheep; D014251:Trichostrongyloidea / Q000648:ultrastructure*