Morphology of the Digestive System in the Wood-Feeding Termite Nasutitermes takasagoensis (Shiraki) [Isoptera: Termitidae]

The morphologies of epithelial cells throughout the alimentary canal of the wood-feeding termite Nasutitermes takasagoensis (Shiraki) were examined. The digestive tract consists of four principal portions, which are the foregut, the midgut, the mixed segment and the hindgut. The midgut epithelium is primarily composed of columnar cells and degenerative cells. Most columnar cells have one or more autophagic vacuoles at cell apexes, suggesting a rapid turnover of the midgut cells. In the mixed segment, the mesenteric epithelium occupies half of the gut wall and the proctodeal epithelium covers the remaining wall. Extensive invaginations of the basal membrane are characteristic of the mesenteric columnar cells, suggesting active transport of an ionic fluid. The hindgut can be divided into five segments, the first of which is a simple tube lined with a thick cuticle, termed the first proctodeal segment. The epithelium of the third segment, the paunch, consists of cuboidal cells, which are covered by multiple cuticular layers. The apical membrane of these epithelial cells forms regular invaginations, suggesting that they have an absorptive function. In the anterior paunch, numerous spirochetes are found adhered to the gut wall. Our observations indicate that termites such as N. takasagoensis appear to have developed structures that enable more efficient interactions with intestinal microorganisms, particularly by the elongation and differentiation of the hindgut and the creation of the mixed segment.