HISTOLOGICAL AND HISTOCHEMISTRICAL STUDY ON DIGESTIVE SYSTEM OF POECILOBDELLA MANILLENSIS

The current study investigated the morphological structure and histochemical characteristics of the digestive system of Poecilobdella manillensis. The results showed that the digestive system was consisted of digestive tract and unicellular salivary glands. Digestive tract includes mouth, pharynx, esophagus, crop, intestine, rectum, and anus. Mouth with three triangular arranged jaws inside opens in the central part of anterior sucker. These jaws, constituted by radiation and striated muscle and covered by single serration on ridge, can cut the skin of the host. Single-celled salivary glands opening on the mastoid on either side of the jaw secreted hirudin. The globose pharynx is mainly composed of mucosa, developed muscularis and adventitia from inside to outside. Esophagus is short and narrow with a few goblet cells and a large number of eosinophilic granules on the mucosa layer. There are 10 pairs of contralateral blind sac outstretched from both sides of crop, and the last and longest one extends to both sides of anus. The intestine is no obvious differentiation and can be subdivided into the intestine and rectum. There are several blind sac-like structures in intestinal front cavity, forming inner blind sac in intestine. Mucosa with more glandular cell and developed submucosa is rich in blood vessels and lymphocytes. Rectal cavity is obvious greater than intestinal lumen, while its fold height is lower than that of intestine. A few goblet cells can be seen between epithelial cells. According to AB-PAS staining, four types of mucous cells were observed in digestive system of the P. manillensis: typeⅠ(red), typeⅡ(blue), typeⅢ (purple reddish) and typeⅣ (blue purple). Mucous cells in oral cavity were dominated by type Ⅳ and type Ⅲ with a small amount of type and type Ⅰ. TypeⅢ cells were the major mucous cells in pharynx. There was no mucous cells in esophagus, crop, anterior intestine and rectum. Most of mucous cells in postmedian of intestine were of typeⅠ, but only typeⅡ in anus. We also discussed the relationship between the structural characteristics of the digestive tract of P. manillensis and the feeding habits.