Parasitic adaptation in leech

There are several important modifications or adaptations, which are found in Hirudinaria due to their semi-parasitic mode of life. They are as follows :

 I. The habits of the leech are well adapted for its mode of living. It is generally found in ponds and pools, where cattle and men go for thinking and bathing. To adapt themselves they do not feed only on a special genus or host. Their diet is also adapted to different periods of their existence.

2. Both ends of the body are provided with suckers, which are the clinging organs by which leech gets firm grip of the host. These suckers, are also helpful for locomotion.

 3. Parapodia and setae are completely absent, because there is no need of these organs. Thus, the host remains unaware of the parasite.

 4. There are three jaws inside the mouth. These act as semicircular jaws and cause a 1'-shaped wound in the skin of the host Through this wound blood is let out.

5. Blood is sucked up by pharynx as it acts as a suction pump.

6. Salivary glands produce hirudin, which does not allow the blood to coagulate. Thus, a continuous supply of the blood is maintained.

7. The chances of getting the host are rare; therefore there is a special mechanism of storing the food in the crop after a meal. Leech may not get food for several months or a year. At a time, leech can store food three times its own weight and this is for several months. Crop is therefore, very long and is provided with lateral pouches.

8. Blood passes from the last chamber of the crop through a sphincter into the stomach very slowly. The digestion is also very slow, therefore, blood stored in crop gives nourishment to the leech for several months. Due to this reason there is not elaborate secretion of digestive juices and enzymes.

9. Reproduction is also well-adapted for the parasitic mode of life. In a cocoon, there are 1 to 24 embryos.

10. The whole process of development is very quick as it takes about a fortnight. Eyes are also present, which are sensitive to alteration of light.