Ultrastructure of the gut caecal epithelium of Pricea multae (Monogenea: Polyopisthocotylea).

Ultrastructural observations of the gut caecal epithelium of Pricea multae revealed the presence of pigmented and non-pigmented digestive cells. The pigmented digestive cells were separated by a connecting syncytium and appeared elongated, with numerous vesicles appearing toward the apical cell surface. They were characterised by granular inclusions in the form of electron-dense pigments, which were eliminated by exocytosis. These cells and their lamellar connecting syncytium were observed projecting into the gut lumen. Transverse sections of the gut epithelium revealed intact portions of digestive cells lying in the lumen. Endocytosis at the apical surface of the pigmented digestive cells gave rise to the formation of granular inclusions, which appeared as electron-dense pigments confined to lysosomal vesicles within the digestive system. Electron X-ray microanalysis indicated these granules were primarily composed of iron, demonstrating that P. multae is a blood-feeder. The connecting syncytium, while probably involved in a structural, supportive role, may additionally function in the absorption of micromolecular nutrients from the host blood meal.