Retrograssive metamorphosis

 

Retrograssive metamorphosis



Metamorphosis is a process by which a larva undergoes several changes to be transformed into an adult. This phenomenon is shown by many non-chordates and some chocolate animals. The individuals of chordates phylum euchordata show special type of metamorphosis known as retrographic metamorphosis. In retrograssive metamorphosis the larva posses advance characters which are lost during the development and the adult is either celentery or degenerated with primitive characters. And this type of metamorphosis shows introgation or degredation from larva to adult, hence it is reffed to as retrogressive metamorphosis. On the other hand the other type of metamorphosis in which a less developed larva changes into a more advanced adult is called progressive metamorphosis.

    Individuals belonging to urochordata are marine, celentery bag like creatures which remain attached to roti substratum throughout their life. Their larva on the other hand is active, tadpole like in share and has the imp. Chordate character such as gill clelts notochord and tubular nerve cord. The larva are developed throughout the external fertilization of hormophrodite individual and they grow up to about 1mm.

         The important Morphological changes in urochordata during the retrograssive metamorphosis are-

  1. The larva attached to the substratum with the help of enhesive pepitilae head downward and tail upward.

  2. The tail started to disappear along with the notochord.

  3. The coastal part of the nervecord also decreases or disappear.

  4. The vidual cell and steticyst of the cerebrate vesicle also dissapear.

  5. The central part of the nervous systems rise to the adult ganglion and to the neural gland 

  6. The muscle in the coudal region degenerate.

  7. The trunk region becomes brooder. 

  8. The mouth is shifted from the attachment.

  9. The no. Of gills slits increases.

  10. The pharyngeal portion differentiates into parts, it also increases in size.

  11. The intestine becomes functional and atrial opening is formed on the opposite side of oral aperture.

  12. Grounds and gonoducts also developed.

  13. The thick covering of test develops around the animal. 

Through it is refered as ratrogesive metamorphosis solve of the morphological changes mentions here are actually progressive . Due to this metamorphosis the free swimming large ultimately settle as a fixed location for the rest of the celentery life.



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