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Metamerism, in biology, is the linear sequence of body segments found in insects, or tapeworms.
- Metamerism can be defined as the repetition of homologous body segments.
- It can often be seen in Annelids, including leeches, earthworms, tubeworms and more.
- In the case of Zoology, metameric segments are usually referred to as somites or metameres, while in Botany, they are usually referred to as metamers or phytomers.
- There are two main types of metamerism in animals: Homonomous and Heteronomous.
Key Terms: Metamerism, Locomotion, Metamers, Somites, Phytomers, Homonomous Metamerism, Heteronomous Metamerism
What is Metamerism?
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In Biology, “Metamerism is the condition of possessing or forming a linear series of body segments.”
- For example, the metameres of earthworms and the metamerism that can be seen in vertebrates at an embryonic stage.
- This process is important in biology as it helps in advanced locomotion.
- Metamerism leads to metamers, which are also known as Somites.
Metamerism
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| Classification of Plants | Class – Osteichthyes | Angiosperms |
Types of Metamerism
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Metamerism is different for animals and plants. While it is less complicated in the case of plants, the animal metamerism can be categorized in two types mostly- Homonomous Metamery and Heteronomous Metamery.
Animal Metamerism
In the case of animals, it can be categorized in two types- Homonomous Metamary and Heteronomous Metamary.
- Homonomous Metamary: Homonomous Metamery can be defined as a strict serial succession of metameres. This kind of metamary can be further divided into two categories- True Metamerism and Pseudo Metamerism.
- True Metamerism: In this kind of metamerism, the parts of the bodywork collectively work for the whole organism. In this case, the body parts stay well connected. For example- Earthworms (i.e. annelids).
- Pseudo Metamerism: In this kind of metamerism, the repeated part of the body usually works independently. In this case, there is no coordination between the body parts. For example- Tapeworms (Cestoda).
- Heteronomous Metamery: Heteronomous metamery can be defined as the metameres that are combined to perform the same task.
- For example, in the case of insects, 5, 3, and 11 metamers can be found in its head, thorax, and abdomen.
- The process through which the entire groups of metamers are combined is called tagmatization.
Plant Metamerism
One of the many segments that contribute to the formation of a shoot or into which a shoot can be resolved is referred to as a metamer. In this case, many “phytomers” or “phytons” can be seen, and every one of them comprises an internode along the upper margin of the leaf.
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Other Types of Metamerism
Metamerism can be categorized in some other subcategories as well. For example,
- External Metamerism: In this case, no partition in the internal part can be observed in this case. For example- Arthropods.
- Internal Metamerism: In this case, the metamerism can be visible in the embryo, and is limited to the nervous, muscular and skeletal system of the plant. For example- Vertebrates. Though there are some exceptions. For example- in Annelids, both internal and external metamerism are visible.
- Complete Metamerism: In complete Metamerism, the entire segment remains visible.
- Incomplete Metamerism: In this case, the segments are not entirely visible.
Metamerism Characteristics
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Here are some of the mentionable features of metamerism-
- Metamerism is always restricted to the intermediate segments, with the exception of the anterior Acron and posterior telson.
- Each metamer appears identical to the other.
- Together, they function as a single unit.
- All parts of the bodywork coordinatedly together.
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|---|---|---|
| Five Kingdom Classification | Phylum Chordata Classification | Herbivores And Carnivores |
| Coelom | Phylum – Aschelminthes | Phylum – Hemichordata |
| Living Fossil | Difference Between Biology And Zoology | Kingdom Animalia |
Things to Remember
- In Biology, the linear sequence of body segments found in insects, tapeworms, and the like is normally referred to as metamerism.
- There are two types of animal metamerism: Homonomous Metamary, Heteronomous Metamary.
- Metarism is restricted to the intermediate segments, with the exception of the anterior acron and posterior telson.
- Metamerism is known to lead to metamers, also called Somites.
Previous Year Questions
- Besides annelida and arthropoda, the metamerism is exhibited by…
- Metameric segmentation is the characteristic of…
- The segments of earthworms are…
- Metameric segmentation is the characteristic feature of phylum…
- In Pinus; the pollen grain has 6 chromosomes then in its endosperm... (NEET 1992)
- Dichotomous branching is found in (NEET 1999)
- Kingdom Animalia is characterised by... (AIIMS 2011)
- Select the correct statement... (NEET 2016)
- Scyphozoan medusae are commonly known as... (COMEDK UGET 2010)
- External fertilization occurs in majority of... (DUET 2009)
Sample Questions
Ques. What is the biological definition of Metamerism? (1 Mark)
Ans. As per biological definition, metamerism can be described as “Metamerism is the condition of possessing or forming a linear series of body segments.”
Ques. Explain the concept of Metamerism in Biology. (2 Marks)
Ans. In the case of biology, the linear sequence of body segments found in insects, tapeworms, and the like is normally referred to as metamerism.
To be specific, in the case of Zoology, metameric segments are usually referred to as somites or metameres, while in Botany, they are usually referred to as metamers or, more concretely, phytomers.
Ques. What are the salient features of Metamerism? (3 Marks)
Ans. Though, Metamerism is one kind of isomerism, in biology, it can be defined as the linear sequence of body segments found in insects, tapeworms, and the like is normally referred to as metamerism. Here are the salient features of metamerism in biology-
- Metamerism is always restricted to the intermediate segments, with the exception of the anterior acron and posterior telson.
- Together, they function as a single unit.
- All parts of the body work coordinately together.
- Each metamer appears identical to the other.
Ques. What are the main types of animal metamerism? (2 marks)
Ans. Animal metamerism can be divided into two categories-
- Homonomous Metamary
- Heteronomous Metamary
Ques. Explain Animal Metamerism. (5 Marks)
Ans. In Zoology, metameric segments are usually referred to as somites or metameres. In the case of animals, it can be categorized into two types: Homonomous Metamary and Heteronomous Metamary.
- Homonomous Metamary is a strict serial succession of metameres. This kind of metamary can be further divided into two categories- True Metamerism and Pseudo Metamerism.
- True Metamerism: In this kind of metamerism, the parts of the bodywork collectively work for the whole organism. In this case, the body parts stay well connected. For example- Earthworms (i.e. annelids).
- Pseudo Metamerism: In this kind of metamerism, the repeated part of the body usually works independently. In this case, there is no coordination between the body parts. For example- Tapeworms (Cestoda).
- Heteronomous Metamery is the metameres that are combined to perform the same task. For example, in the case of insects, 5, 3, and 11 metamers can be found in its head, thorax, and abdomen.
Ques. In which animal both internal and external metamerism are visible? (1 Mark)
Ans. In Annelids both internal and external metamerism can be visible.
Ques. Metamerism is one type of body segmentation and is the characteristic of annelida. Explain the statement. (2 Marks)
Ans. In Annelids, metamerism refers to a linear sequence of body parts. A somite or metamere can be described as each section or piece. Homologous organs, such as nephridia, nerves, muscles, reproductive organs, appendages, and so on, are serially repeated in the case of metamerism. Since each segment coordinates with the others, they form a single functional unit.
Ques. What are the other types of Metamerism? (3 Marks)
Ans. In biology, the linear sequence of body segments found in insects, tapeworms, and the like is normally referred to as metamerism. Apart from the main categories, Metamerism can also be categorized in some other sub-categories as well. They are-
- External Metamerism: In this case, no partition in the internal part can be observed in this case. For example- Arthropods.
- Internal Metamerism: In this case, the metamerism can be visible in the embryo, and is limited to the nervous, muscular and skeletal systems of the plant. For example- Vertebrates.
- Complete Metamerism: In complete Metamerism, the entire segment remains visible.
- Incomplete Metamerism: In this case, the segments are not entirely visible.
Ques. “Bilateral symmetry, metameric segmentation, coelom and open circulatory system are the features of Arthropoda”- Explain if this statement is true or False. (2 Marks)
Ans. This statement is true, because, The largest and most diverse phylum of the animal kingdom is Arthropoda., which includes Myriapods, insects, arachnids, and crustaceans as well. Their body can be divided vertically into two mirror images, resulting in bilateral symmetry. In this case, their internal organs and appendages were serially repeated in each segment of their metameric segmentation. They have open circulatory systems because they are eucoelomate, i.e. they have a true coelom.
Ques. Who discovered metamerism? (1 Mark)
Ans. This idea of metamerism in living body was first proposed by Hyman & Goodrich. According to this theory, “the body parts of animals like coelom, blood vessels, nephridia muscles etc. will be repeatedly formed with septa in between them.” From this core idea, further studies about this topic were conducted.
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