Ultrastructure of the tegument and penetration glands of developing procercoids of Haplobothrium globuliforme Cooper, 1914 (Cestoda: Haplobothrioidea)

Developing procercoids of Haplobothrium globuliforme were examined using transmission electron microscopy. Procercoids require 12–20 days, at approximately 20 °C, to develop to the infective stage. Six-day-old procercoids have a microvillar tegument and numerous undifferentiated subtegumental cells. In 9-day-old procercoids the cercomer is visible as a distinct appendage at the posterior end. Developing microtriches are evident on the tegument of the larval body. These are long and slender, and bear small electron-dense tips. No degenerating microvilli were evident and the microtriches were never seen emerging de novo from the tegument. Fully developed procercoids, 15 days postinfection, have both robust and slender microtriches at the anterior end of the larva, and only long slender microtriches over the remainder of the body. The cercomer retains a microvillar tegument until the larva is fully developed, at which time the tegumental projections on the anterior-most part of the cercomer bear small electron-dense tips. Penetration glands in the anterior part of the larva contain electron-dense secretory granules. The penetration gland ducts, which extend to the tegument, are lined with microtubules.