Morphology of the Digestive Tract of Cladomorphus phyllinus (Phasmatodea: Phasmidae)

The digestive tracts of insects may indicate life history and phylogenetic relationships among different species. Phasmatodea are chewing herbivores with an elongated body shape, which camouflages them on the vegetation on which they feed. This work evaluated the gut structure of the walking stick insect, Cladomorphus phyllinus (Gray 1835) (Phasmatoidea: Phasmidae), with light and scanning electron microscopy. The digestive tract of C. phillynus is an elongated tube with minimal external anatomical differences along its length. There is a short gastric caeca-like structure in the posterior midgut. The crop is an extensively folded storage organ and the proventriculus is covered by a thick cuticle with spine-like projections, which play a role in grinding food. The midgut has 2 anatomical regions probably involved in digestion and absorption of nutrients. The epithelial cells of the anterior midgut have bubbles of apocrine secretion, while the posterior midgut cells have a striated border. Gastric caecae-like projections are found in the posterior midgut. They are enlarged close to the midgut wall, and follow a thin and long filament, which is free in the body cavity. The epithelial cells lining the gastric caecae-like projections are cuboidal with well development striated borders, suggesting involvement in nutrient absorption. The hindgut is divided in an ileum and a rectum. The ileum epithelial cells are covered by cuticle and have cytological traits characteristic of electrolyte and water absorption. The rectum epithelial cells have no obvious absorptive features, but the rectal pads may be involved in water and electrolyte reabsorption. This work reinforces the concept that the anatomy of gut is related to the diet and body shape, and shows that the general pattern of compartmentalization of digestion in insects was maintained in Phasmatodea, but that it differs from other Orthopteroidea in some aspects.