Published online by Cambridge University Press: 05 June 2009
Leiper in 1908, created the sub-family Trichostrongylinae in his new family Metastrongylidae, for those small intestinal bursate nematodes without a buccal capsule. It included the genera Trichostrongylus, Haemonchus, Nematodirus, Cooperia and Ostertagia. In 1912, he raised the status of this sub-family to family rank as Trichostrongylidae Leiper, 1912. All the original genera in this family have a double ovarian system in the female; Heligmosomum described by Railliet and Henry in 1909, has a single ovary and in 1914, Travassos created a new sub-family Heligmosominae for this and related species.