Morphology and Ultrastructure of the Intestine in a Plant-Parasitic Nematode, Tylenchorhynchus dubius

An unusual feature of the intestine in Tylenchorhynchus dubius is the presence, within the intestinal cytoplasm, of an extensive system of fibrillar bundles consisting of thin (14 nm diam) filaments and thick (70-90 nm diam), rod-like elements arranged in closely packed arrays. The larger of the fibrillar bundles, for which the term "intestinal fasciculi" is proposed, are evident in whole mounts and apparently correspond to the lateral or sinuous canals described in some other tylenchids. The nature and function of fasciculi are not known, but some possibilities are considered. Fasciculi were found in at least seven other species of Tylenchorhynchus. The intestinal cytoplasm also contains the usual sub cellular organelles and large amounts of reserve materials in the form of particulate glycogen and three types of globules. The surface of the cells bordering the lumen is elaborated into numerous microvilli which have central filaments and often bear regular external projections. Although terminal bars delimit the apical margins between cells, the frequent lack of complete lateral boundaries and extensive length of the fasciculi indicate that the intestinal epithelium is a multinucleate mosaic or syncytium.