Sublateral hypodermal chords in Haemonchus (Nematoda: Trichostrongyloidea): description and potential as a systematic character.

Prominent sublateral hypodermal chords (SHC) are described in Haemonchus spp. Four large SHC are located 1 muscle cell away from the lateral chords from the level of the middle of the esophagus to midbody. The SHC are largest in midbody and merge with the lateral chords at about 65% of the body length from the anterior end. With the aid of transmission electron microscopy, a band of nerve tissue was located parallel and medial to the SHC. Haemonchus spp. and Mecistocirrus digitatus have SHC that are so large they can be identified in thick freehand midbody cross sections cut with a cataract knife. Because SHC have not been described in other Trichostrongylidae, their presence in members of the Haemonchinae may have value as a systematic character.