Studies on the host–parasite interface of strigeoid trematodes

Abstract

The adhesive organ of Apatemon gracilis minor Yamaguti, 1933, consists of two lobes lying in a cup-shaped fore-body. The cytoplasmic tegument covering the apposing faces of the lobes is different from that covering their outer surfaces. The covering of the outer surface corresponds to the general tegument present on the rest of the body, whereas that on the inner surfaces is finely pitted and in certain regions is elevated to form a coarse reticulum. This specialized surface is covered externally by a plasma membrane and is in continuity with nucleated cell bodies lying below the basement layer. The cell bodies contain large quantities of granular endoplasmic reticulum as well as several Golgi complexes and numerous mitochondria. Masses of secretion bodies are present and these also occur in the extensions to the external tegument as well as within the external tegument of the lobes. When the parasite is attached the inner faces of the lobes come into contact with the vascular lamina propria of the host. The possible biological role of this specialized host–parasite interface is discussed and it is suggested that this surface specialization may form a morphological basis for the ‘placental’ function suggested for the adhesive organ by earlier workers.The author wishes to acknowledge the research grant provided by the S.R.C. for the purchase of a vacuum coating unit and an AEI EM 6 electron microscope. The progress of this study was greatly facilitated by the excellent assistance of Mr T. Davies and Miss C. Green. The Stereoscan micrographs are published by permission of the Cambridge Instrument Company.