First description of the horse stomach worm, Habronema muscae (Spirurida: Habronematidae) by scanning electron microscopy.

Habronema muscae (Spirurida: Habronematidae) occurs in the stomach of equids, is transmitted by adult muscid dipterans and causes gastric habronemiasis. Scanning electron microscopy (SEM) was used to study the morphological aspects of adult worms of this nematode in detail. The worms possess two trilobed lateral lips. The buccal cavity was cylindrical, with thick walls and without teeth. Around the mouth, four submedian cephalic papillae and two amphids were seen. A pair of lateral cervical papillae was present. There was a single lateral ala and in the female the vulva was situated in the middle of the body. In the male, there were wide caudal alae, and the spicules were unequal and dissimilar. At the posterior end of the male, four pairs of stalked precloacal papillae, unpaired post-cloacal papillae and a cluster of small papillae were present. In one case, the anterior end showed abnormal features.