Equine stomach worm, Drashia megastoma (Spirurida: Habronematidae): first SEM report.

Drashia megastoma (Spirurida: Habronematidae) occurs in nodules in the stomach wall and rarely free in the stomach of the horse, mule and zebra throughout the world. D. megastoma develops in the housefly Musca domestica and causes gastric haemorrhage or even perforation of the stomach. Larvae of this nematode may be found in the lung, skin and eye of the host. Scanning electron microscopy (SEM) was used to study the surface ultrastructure of adult worms of this nematode. In both sexes, the head end was separated from the rest of the body by a constriction. The stoma was infundibuliform with a wall forming two separated lateral vales. The pseudo-labia were not lobed. Around the mouth, four submedian cephalic papillae and two amphids were seen. A pair of ciliated cervical papillae was present, and an excretory pore was observed. There were two lateral alae. In the female, the vulva was opened anteriorly. The caudal end of the male was alate and the spicules were unequal. At the posterior end of the male, four pairs of stalked precloacal papillae, two median precloacal papillae close to the cloaca, two pairs of postcloacal papillae and a cluster of small papillae were present.