Metamerism in annelida in +3 student zoology paper

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·  Prof.- Dr ramakant pradhan 
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METAMERISM IN ANNELIDA
  -    In some animals body is divided into a series of compoctment one behied the other.
-  These componets are called segment.
-       The inner arrengment of segment is called metamerism.
CHARECTERSTICS OF METAMERISM
-       In metamerism each segment is the mirror image of other segment.
-      Each segment contain nepharidia , blood vessels ,reprodactive organ ,nerve and muscle.
-      The segment mark in coporation with all orther segment.
TYPES OF METAMERISM
. A. True metamerism
-       The segment of body is based on segmentation mesoderm.
-      It is found is all annelida charecter and arthropods
-      New segments are found at the posterior and old segment occours at anterior.
  B. Pseudometamerism
-       The segment of body is based on segmentation ectoderm.
-     In pseudometamerism new segment are found at
  Hence the youngest occurs at the anterior end and oldsegment occours at posterior.
-       The segment behaves indipently their is no corporation between segment.


  C. Homonomous
-       It the segment are similar is in segmention is called homonous segment.
-      The homonomus segmentation is not found in existing animal.
-      But few of the anterior segment are always specialised ,this specialisation is called cephalisation.
-      Homonomus is a primitive condition.
EX- Neris
  D. Heteronomus    ---    If the segment are dis similsar in segmentation is called heteronomus segments.
EX- Arthropoda and chordata
E. Externaly metamerism
-      In arthropoda metamerism is external.
-      Internaly the segments are not marked by any partition.
  F. Externaly and internaly metamerism
-       In annelida , the segmentation is marked externaly as well as internaly.
-      Internaly the segments are separated by transvers patition ,called as septum.
  G. Complete metamerism
-       When the segmention seen in all organ,
This metamerism is called as complet metamerism.
  EX- Annelida
  H. Incomplete metamerism
-       When metamerism not seen in all organ,
  This metamerism is called as incomplete metamerism.
  EX- Arthropoda and Chordata

      ORGAN OF METAMERISM

-       There are many theory to explain the origin of metamerism.
They are ;
  a. Cornofission theory
-       A/C to this theory the segmented animal is really chain of individual zooids.
-      Each zooids represent the single segment.
-      These zooids are by transveers fission of an unsegmented ancestor.
-      Zooids are united end to end.
  b. Pseudometamerism in theory
-       A/C to this theory the ancester was unsegmented.
-      It contain the body system separad out along the length of the body.
-      This unsegmented body become segmented by development of septa.
  c. Locomotary metamerism theory
-       A/C to this theory the metamerism is form by the breaking up of the body into segment as a result of swimming movement.   
    SIGNIFICANCE OF METAMERISM
-      Metamerism give many advantages for the animal they are
                               I.            It classifiecd locomotion
                             II.            Metamerism offer division of labous.




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