It is very similar to another species called cooperia oncophora. This means that one must be careful when making an identification. They can only be differentiated by their larval stages. Studies have been done showing that the metabolism of a female may be considerably greater than that of the male. This extra metabolism is required for reproductive activities.
Males are smaller than females.
The book entitled the SEM Guide to Morphology of Nematode Parasites of Vertebrates is an excellent source for viewing the morphology of the species H. Contortus. References Chopra, A.K. 1982.Observations on non-Specific phosphomonoesterases in relation to glycogen content in three nematodes in sheep. Wertjuk, M. 1964. On the infective larvae of the gastointestinal nematodes of sheep, and their identification.pp.361-404. Gibbons, L. 1986.