Developmental study of digestive system of the postembryo disk abalone Haliotis discus hannai Ino

Development of digestive system of postembryo disk abalone Haliotis discus hannai Ino was studied from trochophore larva after hatching to one year old abalone with histological and histochemical methods and electron microscopic observation.Oesophagus appears in early veliger.The epithelial cells of mid oesophagus secrete proteinase in the stage of larva with peritomal.The lateral pouches of mid oesophagus form in the stage of larva with pallial tentacle.In 45d old juvenile,the epithelium of the lateral pouches differ entiates into cells with microvilli,secretory cells and ciliated cells.Crop does not for muntil 45 d old juvenile,and its lumen is larger than stomach lumen in one year old abalone.Stomach forms in early veliger.In creeping larva,single-cell's algae appear in the lumen of stomach.Intestine also formed in early veliger.The epithelium of intestine differentiates respectively into two and five types of cells in larva with pallial tentacle and 45 d old juvenile.Salivary glands appear in the stage of larva with pallial tentacle.Digestive gland appears in early veliger and begins to differentiate into basophilic cells and digestive cells in mid veliger.The acidophilic cytoplasm of basophilic cells is gradually changed into basophilic one.Refractile spherules containing ir on begin to appear in the basophlic cells since the stage of larva with pallial tentacle.A s creeping larva feeds,digestive cells show endocytosis and contain a number of vesicles.The studies show that structure and function of all digestive organs of 45 d old juvenile are basically similar to ones of adult abalone.