On the histochemistry and ultrastructure of the redia ofNeophasis lageniformis(Lebour, 1910) (Trematoda, Acanthocolpidae)

Abstract

Abstract The redia of Neophasis lageniformis within the first intermediate host, the carnivorous prosobranch Buccinum undatum, has been studied by means of light microscope and scanning and transmission electron microscopes. The tegument of the redia is provided with irregular cytoplasmic projections or microvilli-like structures and knobs. Short cilia occur around the mouth and long cilia on the lateral surface. Numerous pinocytotic vesicles in the intestinal cells and in the tegument show that absorption of nutrients takes place through both the intestinal caecum and the external surface. The fine structure of the body wall of the redia is discussed and compared with previous investigations of the ultrastructure of germinal sacs. Histochemical tests showed that the tegument and subtegumentary layer contain acid and alkaline phosphatases, non-specific esterase, and aminopeptidase. The intestinal lumen contains a high concentration of acid phosphatase, and the pharynx is highly non-specific esterase-positive. The light and transmission electron microscopical observations indicate that the host tissue is digested extracorporeally and that the host cells normally are unable to fight this parasite.