Scanning Electron Microscopy of Third- and Fourth-Stage Larvae and Adults of Brugia pahangi (Nematoda: Filarioidea)

Publisher Website
Google Scholar
Abstract
Third- and 4th-stage larvae and adults of the filarial worm B. pahangi were examined by scanning electron microscopy. All stages studied have closely spaced, cuticular annulations over the entire surface, except at the extremities. Cuticular annulations of recently molted worms are narrower than annulations seen late in the preceding stage, but widen as the worm growns. The head bears 8 cephalic papillae in 2 circles of 4 papillae each. There are 2 subdorsal and 2 subventral papillae in each circle. Third-stage larvae bear a central, nipplelike protuberance atop each of the inner, cephalic papillae. Three prominent, terminal, caudal papillae are lost at the 3rd molt. Molting 3rd-stage larvae show irregularities in the cuticular surface and desquamation of the old cuticle. The 4th-stage larva shows a globular head region, numerous tubercles in the anal region, and a pair of terminal, caudal papillae. No sexual dimorphism is seen in either 3rd- or 4th-stage larvae. The vulva appears after the final molt, and there are major changes in the male at this time; tubercles shift to the 1st coil of the tail about 1 mm anterior to the anus, there are 10-12 nipple-bearing, perianal papillae, and the cloaca of the adult appears. The terminal, caudal papillae of adult worms are difficult to visualize and count. The orifice of the mouth is slitlike in the ineffective larva, but becomes triradiate after the final molt. The external orifice of amphids and phasmids could not be visualized.