Fine structure of the pyloric region and of the hindgut in the proturan Neocondeellum dolichotarsum (insecta, protura)

The fine structure of the midgut, pyloric region, Malpighian papillae, and hindgut in the proturan, Neocondeellum , was studied. Midgut cells, rich in rough endoplasmic reticulum and mitochondria, are linked to each other by smooth septate junctions. No peritrophic membrane is visible over the microvilli. The posterior cells of the midgut carry short microvilli and are surrounded by a muscular pyloric sphincter. Behind such sphincter is a wide pyloric chamber that has cells with very long microvilli pointing anteriorly toward the midgut. These cells with their microvilli form a kind of stopper that controls the passage of the intestinal content into the hindgut. The Malpighian papillae have an apical globular secretory region producing proteinaceous material, which is then collected in a microvillate cistern at the proximal end of the cell. A peduncle formed by flattened squamous cells joins each papilla to the hindgut epithelium. The hindgut shows two differently organized regions, both engaged in fluid reabsorption. The principal cells of the anterior region show a system of apical subcuticular cavities into which thin microvilli extend. In the cytoplasm of these cells, there are numerous mitochondria associated with infoldings of the plasma membrane. The principal cells of the posterior hindgut region have bundles of long microvilli beneath the cuticle. Also, these cells exhibit at their base an abundant system of infoldings of the plasma membrane and mitochondria. The results are considered in relation to the phylogenetic relationship between Neocondeellum and other proturan genera.