Histological observations on the development of digestive tract in <italic>Tachypleus tridentatus</italic>

Abstract

In this study, paraffin sections and H-E staining were used to study the individual development of alimentary canal of <italic>T</italic>. <italic>tridentatus</italic> at 15 days old, 30 days old, 60 days old, the second instar and adult. Results showed that the structure of digestive tract of <italic>T</italic>. <italic>tridentatus</italic> at 15 days old was not clearly distinguished. The esophagus, stomach, midgut and rectum were similar in structure. Only mucous membrane was clear, and mucous folds were relatively short. When <italic>T</italic>. <italic>tridentatus</italic> was 30 days old, the mucous epithelium of esophagus and stomach showed dark bands, the muscle fibers of esophagus extended in a ring, and the muscle bundles of stomach were thickened. The mucous epithelium of the middle intestine and rectum had a striate border at the top, and the muscular fiber bundles were thickened. When <italic>T</italic>. <italic>tridentatus</italic> was 60 days old, the dark bands at the top of the mucosa epithelium of the esophagus and stomach developed into striate margins, with increased esophageal muscle fibers and thickened gastric myofilament bundles. The mucosa fold of the midgut and rectum increased in height and number, and the pigmentation of the striate border deepened. The digestive tract of the second instar <italic>T</italic>. <italic>tridentatus</italic> was composed of mucous layer, submucous , muscle layer and serosal layer, and the tissue structure was basically well-developed. With the gradual improvement of tissue structure, the number of folds of esophagus and gastric mucosa increased significantly to 9-15, and the striate border at the top of the mucosal epithelium developed into chitin layer. The number of folds in the mucosa of the middle intestine and rectum increased rapidly to 10-12, and the epithelial striatum of the mucosa of the middle intestine thickened, with little tin layer, and the epithelial striatum of the rectum developed into chitin layer. The structure of digestive tract of adult <italic>T</italic>. <italic>tridentatus</italic> was complete, and the mucous layer, submucous layer, muscle layer and serous membrane of digestive tract were obviously thicker than that of early stage. Results showed that the tissue structure of the alimentary canal of <italic>T</italic>. <italic>tridentatus</italic> was basically developed at the second instar, and the tissue structure of each layer was thickened with age, which was suitable for its living habit.