Ultrastructure of the esophageal procorpus in the plant parasitic nematode, Tylenchorhynchus dubius, and functional aspects in relation to feeding

The ultrastructure of the procorpal region of the esophagus in the plant parasitic nematode, Tylenchorhynchus dubius, is described and interpreted in terms of function. The anterior procorpus has a small central core comprising attenuated processes of the esophageal cells that subtend the procorpal lumen and an outer sleeve comprising portions of the protractor muscle and marginal cells that are associated with the stylet base. Retractor muscles are absent, but fine filaments extending back from the posterior edge of the stylet knobs may play a role in retraction. Longitudinally oriented bundles of microtubules within both the marginal and, to a lesser extent, the muscle cells of the outer sleeve are a prominent feature of the anterior procorpus. Their function is unknown. The cytoplasmic extension ("dorsal duct") of the dorsal esophageal gland cell contains microtubules which lie parallel to the long axis of the extension and may participate in the transport of the secretory granules. The valvular end-apparatus of the terminal duct of the dorsal gland extension is described and a mechanism of its action is proposed. Structures filled with small vesicles resembling neurosecretory packets, which appear to be expanded nerve endings, are intimately associated with the ampulla of the dorsal gland extension.