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What is a Leech?

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In the biological classification system, living creatures are classified into two kingdoms- plant kingdom and animal kingdom. There are ten phyla in the animal kingdom. Leech is a worm of phylum Annelida and class Clitellata. It is a segmented parasitic worm. Leech scientific name is Hirudinaria granulosa. It belongs to the subclass Hirudinea. Leech has a soft, segmented, and muscular body, which can lengthen and contract. Leeches have a body structure, which is formed with multiple rings. Leech has suckers in both ends of the body. It uses the suckers as hypodermic needles. They have one to four pairs of eyes. Leeches live in freshwater habitats, marine or terrestrial environments. Leech is a parasite, which sucks blood from its host to survive. The digestive system of the leech contains a pouch. In this article, we will discuss the structure of leech, leech anatomy, characteristics, reproduction system, blood circulatory system, excretion, and other things of leeches in detail.

Leech in Animal Kingdom

The animal kingdom contains various kinds of living creatures such as worms, insects, mammals, etc. Leech is a segmented parasite worm of the animal kingdom. Leech animal harms its host for its survival. Leech is classified in a specific phylum, class, and subclass. It belongs to the phylum Annelida. The class is Clitellata and the subclass is Hirudinea. There are different types of leeches. The scientific name of all the leeches is given according to their higher classification. There are almost 700-1000 types of leeches in the world. Generally, the leeches are divided into four main types according to their living place, which are freshwater leeches, terrestrial leeches, marine leeches, and leech mouth types.

Classification Characteristics Of Leeches

In the animal kingdom, all the animals are separated into different phyla depending on some particular properties. Leeches are under the phylum Annelida for some specific properties. The classification characteristics of leeches are-

  • The body of leeches is formed with several ring-like structures.

  • The execution organ is nephridia.

  • Leeches have a closed circulatory system.

  • Leeches have real Silom covered with mesoderm.

  • The nervous system is formed with a pair of cerebral ganglia and two axial nerves.

Habitation of Leeches

Leeches live in the land mainly. They can also be found in the water. The four main habitats of the leeches are freshwater, land environment, terrestrial environment, marine environment. Leeches have different characteristics depending on their habitation. In all the places, they live on the other animals by the segmented parasitic system. They choose their host depending on the habitats. Also, habitat is the main factor in the classification of leeches. The leeches can be of different types depending on their habitats. In different atmospheric areas, the leeches can be of different types.

Food of Leeches

Leech is a segmented parasitic animal. It survives on the blood of other animals such as mammals, fishes, frogs, etc. They choose their host depending on the environment they are living in. Leeches detect their prey by the vibration of the land or the water. They attack the host with their mouth or tail. The suckers located on both ends help the leeches to suck blood from the host’s body. They release hirudin, an anticoagulant, during sucking to prevent blood from clotting. They release an anaesthetic into the host’s blood so that the host cannot be aware. 


When the leech sucks blood with the mouth, the jaws help to hold onto the host. They use sharp teeth to sink in. Then it sucks blood with the front sucker. The posterior sucker helps the leech to move quickly and climb the host’s leg. Then it uses the front sucker to suck the host’s blood. The posterior sucker is not used to suck blood. Leeches suck blood till it is full. Apart from blood, leech eats small animals, worms, snails, etc. Generally, the food is dependent on the type of leech.

Structure of Leeches

Leeches have a body formed with several ring-like structures. They have a total of 34 segments in their body. The length of the body is around 20 cm, which is equal to 8 inches. It becomes longer than the usual size when the leech stretches. They have one to four pairs of eyes in the anterior end. Leeches have two suckers in the front end and the back end. The sucker attached to the mouth is called the anterior sucker. The sucker attached to the tail is called the posterior sucker. The posterior sucker helps to attach to the host and the anterior sucker helps to suck blood. The entire volume of the body becomes large after sucking the host’s blood.

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Leech Anatomy

Leeches have all the anatomical characteristics of Annelida. The body structure is ring-like. Leeches have suckers in their body. The length of the body can differ depending on the type of leech. It can be from 20 cm to 45 cm. The length of the sucker can be up to 10 cm. The anterior sucker helps to suck blood from 30 minutes to 6 hours. The body weight becomes several times the original weight after sucking. Leeches have 9 pairs of testicles, 10 stomachs, 32 brains, several hundred teeth. They have a pouch-like structure in the digestive system. The blood circulatory system is closed. For locomotion, leeches lack septa, setae, parapodia. They have clitellum to secret a viscid sac for depositing eggs. It is located 2 cm behind the anterior end. The saliva of leech contains 100 pharmacologically active substances.

Digestive System of Leeches

Leeches are segmented parasites. They live by eating the blood of other animals in their habitats. They suck blood from the host’s body and survive on it. Leeches also eat small animals, worms, snails, etc. they store the blood or food in a pouch. The digestive system contains the pouch to store food for a long time. The digestive system has an alimentary canal and salivary glands. The alimentary canal is a straight tube, which starts from the mouth and ends at the anus. The associated salivary glands are located in different parts of the alimentary canal for different functions of digestion. Leeches suck blood from the host’s body slowly and store it in the pouch for future use. 

Reproduction System of Leeches

Now, we are going to discuss the reproduction system of leeches. Leech is hermaphroditic. They have functional reproductive organs of both sexes in one individual’s body. They reproduce in spring in either sexual or asexual processes. Leeches are not self-fertilizing. The sperm of one individual can fertilize the eggs of another individual. The eggs are covered with a cocoon, which is deposited in the water or land before fertilization. Leeches secret clitellum to deposit eggs. Sperm breaks into the cocoon and fertilizes the eggs. Leeches make gamete during sexual reproduction. Also, asexual reproduction can happen without gamete.

Excretory System of Leeches

The excretion organ of the leech is nephridia. Among the seventeen pairs of nephridia, the anterior six pairs are located in the pre-testicular segments. These pairs are called pre-testicular nephridia. The remaining pairs are called testicular nephridia. Leeches complete their excretion process with the help of these pre-testicular and testicular nephridia. In leeches, nephridia perform the same function as vertebrate kidneys. It removes metabolic wastes from the leech’s body.

Type of Leeches

There are many leech species present in the world. They can be classified mainly into four types depending on their habitats. Four types are freshwater leeches, terrestrial leeches, marine leeches, and leech mouth types. Freshwater leeches live in the water streams, ponds, lakes, rivers. It is the common leech across all the continents. Terrestrial leeches live in the land with high humidity. They need high moisture to protect their mucus. Marine leeches are mainly found in the oceans. Apart from the environment leeches, there are leeches identified by their mouth. The mouth structure depends on the prey’s type, which is directly related to the environment. 

Did You Know?

Now, we are discussing some unknown facts about leeches.

  • Though leeches suck blood for survival, all the leeches don’t suck blood.

  • Leeches can be found everywhere in the world. It can be the land or the water area of all the continents.

  • Leeches can grow up to 18 inches by sucking blood and their weight can be several times the original weight.

  • Despite being hermaphroditic, leeches are not self-fertilizing.

  • The saliva of leeches contains about 100 types of pharmacologically active substances. These substances are used in medical science.

  • The protein present in the saliva of leeches helps in reducing pain. The protein was used during the civil war as a major form of therapy.

FAQ (Frequently Asked Questions)

1. What are the Leech Characteristics of Classification?

Ans: All the animals of the world are classified under the animal kingdom depending on their characteristics. Every animal has their phylum, class, and subclass. Leeches are not an exception. Leech phylum is Annelida. The class and subclass of leech are Clitellata and Hirudinea. The position of leeches in the animal kingdom is given depending on some characteristics, which are-

  • The body of leeches is formed with many ring-like structures.

  • The excretion organ is the nephridia.

  • The blood circulatory system is closed.

  • Real Silom with the mesoderm cover is present.

  • The nervous anterior and posterior suckers in their body.

  • Leeches have anterior and posterior suckers in their body. 

2. How Do Leeches Suck Blood from the Host?

Ans: Leeches are segmented parasitic animals. They survive by sucking blood from the host’s body. They detect their host by the vibration of land or water. Also, they can smell carbon dioxide emitted by the host. Leeches suck blood with the help of two suckers of their body. The posterior sucker helps to move quickly and climb the host’s leg. Then they attach themselves by the jaws and hold on to the host. They sink in the sharp teeth in the host’s blood and sucks with the anterior sucker. Leeches release an anaesthetic into the host’s blood so that the host stays unaware of the blood loss.

3. Describe the Body Structure of the Leech.

Ans: Leeches have a specific body structure. The body is formed with many ring-like structures. There are a total of 34 segments in the body. Usually, the length of the body is 20 cm. it becomes longer when leeches stretch. Leeches have two suckers in their body- anterior sucker and posterior sucker. The sucker attached to the mouth is the anterior sucker. It is used to suck blood from the host’s body. The sucker attached with the tail is the posterior sucker. Leeches use it to be attached to the host. Leeches have one to four pairs of eyes in the anterior end. Also, the other structural characteristics of Annelida are present in leeches.

4. What are the Different Types of Leeches?

Ans: Several leech species are present in the entire world. All the species can be classified mainly into four types. Four types of leeches are freshwater leeches, terrestrial leeches, marine leeches, and leech mouth types. They are classified depending on the habitats.

  • Freshwater Leeches: They are the most common leeches and live in lakes, ponds, rivers, streams. 

  • Terrestrial Leeches: They live in high humidity lands. The high moisture protects their mucus. 

  • Marine Leeches: They are mainly found in the oceans.

  • Leech Mouth Types: Apart from the environmental leeches, there are leeches classified by the type of mouth. The mouth type depends on the types of prey.

5. Discuss the Reproduction Process of Leeches.

Ans: Reproduction is an essential process for every animal. Every animal has their reproduction process. Here, we are discussing the reproduction process of leeches. They reproduce in both sexual and asexual processes. The reproduction time of leeches is spring. Leeches are hermaphroditic. They have functional reproductive organs of both sexes in one body. They are not self-fertilizing. The sperm of one individual can fertilize the eggs of another individual. The eggs are covered with cocoons and deposited in the water or land before fertilization. Clitellum helps in the deposition. Sperm breaks into the cocoon and fertilizes the eggs. Leeches may not form gamete for reproduction and complete it in the asexual method.