Hirudinea - Feeding and Digestion in Annelids
Hirudinea involves free living and ectoparasitic leeches. Leeches are blood suckers. The digestive system contains a preoral chamber which accommodates a sucker at the base of which lies the triradiate opening, the mouth. The walls of the mouth are embedded along with jaws, three in number, of which one is mid-dorsal and the other two ventro-lateral. Each jaw bears a row of minute teeth. The alimentary canal contains a thick muscular pharynx followed by a short oesophagus. Unicellular salivary glands are found on either side of the pharynx. The oesophagus is followed through a crop, an extensive sac consisting of 10 to 11 chambers, the chambers communicate along with each other by openings surrounded by sphincters. Each camber is gave with a pair of backwardly directed lateral caeca. There is a progressive increase in the size of caeca, the anterior pairs being smaller in size, and the caeca of last chamber being the largest. Following the crop, there is a small round stomach with a much folded inner wall, and the stomach in turn leads into a narrow intestine the inner wall of that is provided with horizontal and transverse folds to increase the absorptive surface. The intestine is followed by rectum that opens outside by anus.