Functional morphology of the tegument ofCorrigia vitta (Trematoda: Dicrocoeliidae)

Abstract

The tegument ofCorrigia vitta has been examined systematically by scanning and transmission electron microscopy. Its basic structure is of typical platyhelminth plan but there are several features of surface morphology which distinguish the worm. The tegument is microvillous and in the anterior dorsal region bears numerous small protuberances with a fine fibrous content. Non-ciliated sensory papillae, containing a bulbous nerve ending and covered by tegument, occur in distinct annular patterns on the suckers. An infolding of body tegument lines the foregut and is confluent with the gastrodermis. The transition region is characterised by the elevation of tegumental nuclei to the surface syncytium, and by the appearance of an organized granular endoplasmic reticulum and Golgi elements in the cytoplasm. There is also a gradual disappearance of tegumental secretory bodies which is coincident with a reduction in the amount of surface glycocalyx. Tegumental mitochondria vary in size and number and show a distinct regional distribution. Ventral tegument mitochondria are numerous, with many cristae, and stain strongly for cytochrome oxidase; those in the dorsal tegument and foregut have few cristae and stain only moderately for the enzyme. Results are discussed with respect to surface function and the close association of ventral tegument with pancreatic duct epithelium.