explain terms with examples
.True metamerism
.homonomus metamerism
.hetronomous metamerism
.pseudo-metamerism
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❤. True metamarism : It is a type of metamerism in which segments are true if we cut one segment from the body then the organism will die definitely.
❤.Homogeneous metamarism : in this metamarization the segments are equal and equal in structure same in structure. place of segments on pics
❤. Heterogeneous metamarism : in this type of metamerism the place of segments are not fixed and they are not similar in structure
❤. Pseudometamarizm : in this type of metamerism segments are independent of the body if we cut any segment then organism will not die the body of organism will not affect.
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❤. True metamarism : It is a type of metamerism in which segments are true if we cut one segment from the body then the organism will die definitely.
❤.Homogeneous metamarism : in this metamarization the segments are equal and equal in structure same in structure. place of segments on pics
❤. Heterogeneous metamarism : in this type of metamerism the place of segments are not fixed and they are not similar in structure
❤. Pseudometamarizm : in this type of metamerism segments are independent of the body if we cut any segment then organism will not die the body of organism will not affect.
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jhaShivani:
thank u
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that's a great answer dear :)
....Thanks locomaniac....⭐⭐⭐
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4
1. True Metamerism:
The true metamerism is one in which the segmentation of the body develops by the segmentation of the mesoderm. It occurs in annelides, arthropods and in most chordates. The body of annelids consists of a number of segments and the number remains constant in a particular species except in certain cases of asexual reproduction. New segments are not added to the body after maturation.
That means after the embryonic stage all the segments become the same age. Moreover, the segmental structures are interdependent and integrated so that the individuality of the body is preserved. New segments arise at the posterior end in front of the pygidium. Hence, newer segments occur at the posterior end and older segments remain just behind the head.
2. Homonomous Metamerism:
If the segments or somites of the animal are all alike, the’ segmentation is called homonomous metamerism. It is seen in annelids. Each metamere contains segmental blood -vessels, nerves, nephridia and coelomoducts. This is a primitive type of segmentation and is not found in any existing animal because a few anterior segments are specialised to form the head which is called cephalization.
A well-defined and well-organised head is lacking in annelids. However, formation of a ‘head’ is suggested in polychaetes by anteriorly placed structures and their association with parapodial cirri.
In some polychaetes transformation of one or two post-oral segmental parapodia into protostomial cirri has occurred. This transformation is accompanied by a shift of these post-oral segments and their ganglia anterior to mouth (pre-oral), resulting some sort of a brain formation. Cephalization in true sense is absent in annelids.
3. Heteronomous Metamerism:
In arthropods and chordates the segments of the body are dissimilar in different body regions and restricted only to certain organs. This type of metamerism is called heteronomous metamerism .
4. Pseudo-metamerism or Strobilization:
In contrast to true metamerism, pseudo-metamerism or strobilization is seen in tapeworms (Platyhelminthes) where segmentation of the body takes place by the segmentation of the ectoderm. The body consists of a number of segments or proglottids which varies in different individuals of the same species.
New segments are added to the body throughout life. The proglottids or segments differ in the degree of development. The segments or proglottids are functionally independent or self-contained units and new segments are always formed and there is no cooperation between the segments. The new segments are formed at the anterior end, just behind the scolex.
The true metamerism is one in which the segmentation of the body develops by the segmentation of the mesoderm. It occurs in annelides, arthropods and in most chordates. The body of annelids consists of a number of segments and the number remains constant in a particular species except in certain cases of asexual reproduction. New segments are not added to the body after maturation.
That means after the embryonic stage all the segments become the same age. Moreover, the segmental structures are interdependent and integrated so that the individuality of the body is preserved. New segments arise at the posterior end in front of the pygidium. Hence, newer segments occur at the posterior end and older segments remain just behind the head.
2. Homonomous Metamerism:
If the segments or somites of the animal are all alike, the’ segmentation is called homonomous metamerism. It is seen in annelids. Each metamere contains segmental blood -vessels, nerves, nephridia and coelomoducts. This is a primitive type of segmentation and is not found in any existing animal because a few anterior segments are specialised to form the head which is called cephalization.
A well-defined and well-organised head is lacking in annelids. However, formation of a ‘head’ is suggested in polychaetes by anteriorly placed structures and their association with parapodial cirri.
In some polychaetes transformation of one or two post-oral segmental parapodia into protostomial cirri has occurred. This transformation is accompanied by a shift of these post-oral segments and their ganglia anterior to mouth (pre-oral), resulting some sort of a brain formation. Cephalization in true sense is absent in annelids.
3. Heteronomous Metamerism:
In arthropods and chordates the segments of the body are dissimilar in different body regions and restricted only to certain organs. This type of metamerism is called heteronomous metamerism .
4. Pseudo-metamerism or Strobilization:
In contrast to true metamerism, pseudo-metamerism or strobilization is seen in tapeworms (Platyhelminthes) where segmentation of the body takes place by the segmentation of the ectoderm. The body consists of a number of segments or proglottids which varies in different individuals of the same species.
New segments are added to the body throughout life. The proglottids or segments differ in the degree of development. The segments or proglottids are functionally independent or self-contained units and new segments are always formed and there is no cooperation between the segments. The new segments are formed at the anterior end, just behind the scolex.
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