According to their parasitic mode of life leeches show a number of adaptations in their morphology, habit and habitat:
1. Habit and habitat:
Leeches swim actively in search of hosts and inhabit in such a pond or lake where cattle, men and other vertebrates visit frequently.
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2. Slime glands:
These are present in body wall. Their secretion keeps the body moist and slippery so that the host can’t remove it easily while it sucks blood.
3. Suckers:
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These are the organs that help in locomotion as well as in making firm adhesion to the host’s body while feeding.
4. Jaws and pharynx:
Triradiate jaws are equipped with denticles, able to make incision in the skin of the host. A muscular suctorial pharynx works as a suction pump to suck more and more blood, oozing out from the wound.
5. Hirudin:
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Hirudin is an anticoagulant, secreted by salivary gland when it sucks the blood to prevent it from coagulation. It faciliates the feeding.
6. Spacious crop:
The availability of the host to the leeches is not regular. Therefore its digestive tract is modified in order to store a great quantity of blood in a single meal whenever it gets chance to feed.
To accomodate the large amount of blood the crop is spacious, thin walled, elastic and capable of great dilation.
7. Slow digestion:
Blood from crop is poured into stomach drop by drop because digestion is very slow. So that after a full meal a leech can stay for one year or more without feeding.
For this reason also, leeches lack elaborate digestive juices and enzymes for digestion.
8. Sense organs:
These are well developed and provide the animal with greater opportunities of life.
9. Hermaphroditism:
This doubles the rate of reproduction as after copulation both individuals lay eggs.
10. Development:
It takes place in cocoon with full safety and efficiency. It is very quick and takes only a fortnight.
