This male Heligmosomoides is a good illustration of why many parasitology students (and even someprofessors) avoid nematode morphology if they can at all help it! The copulatory bursa at the posterior end of the worm (lower left) is prominent, as are the muscular rays which support it and help grip the female during mating. Most Strongylata have a similar bursa with an identical number of muscular rays, but the branching pattern of the rays differs between species and is extremely important in the taxonomy of this group. Special mounting procedures must be used to spread out the bursa and view the rays clearly if a specimen is going to be identified. The thin, dark, curved structure emerging from between some of the bursal rays is a spicule.
The anterior end of the worm is at the centre of the coil, and the esophagus is the structure filling the first 1/2 coil of the body. The intestine proceeds from esophagus to anus, but so do coils of the testis and vas deferens, so it is difficult to distinguish them in this photo, or even in a fresh specimen!