Larval%20forms%20of%20trematodes%20%5e0%20cestodes%20ppt%5e (2).pptx

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1. Larval forms of trematodes & cestodes

2. Introduction Phylum platyhelminthes is divided into 3 classses 1. Turbellaria 2. Trematoda 3. Cestoda Trematoda: Animals may be ecto or endoparasites. Commonly called flukes. Body generally elongated and unsegmented. Examples : Fasciola hepatica, schistosoma. Cestoda: Commonly called Tapeworms. Body segmented and ribbon like. Example : taenia solium, hymenolepis.

3. Following are the larval forms of trematoda & Cestoda. 1. Miracidium 2. Sporocyst 3. Redia 4. Cercaria 5.metacercaria ( all 5 are found in Fasciola hepatica). 6. Onchosphere 7. Cysticercus ( found in taenia solium). a

4. 1. Miracidium Larva Free swimming larva of F. Hepatica. It is conical in shape. Cilia present all over the body. Body wall covered by epidermal plates. Apical ganglion, apical papilla present. The larva has 2 protonephridia. Each protonephridium has flame cells & long duct . The duct opens to outside by nephridiophore.

5. 2. Sporocyst larva It is a sac like structure covered by cuticle. Cilia and epidermal cells absent. It has 2 protonephridia which has flame cells. Larva is filled with germ cells.

6. 3. Redia larva. Elongated sac like larva, comes out by rupturing cyst and migrates to liver or digestive gland of snail. Small mouth present at the anterior end. A ring like muscular collar is present which helps in locomotion. Germs cells give rise to new larval stage.

7. 4. Cercaria larva Heart shaped larva with tail. Body covered by Thin cuticle. Mouth surrounded by oral sucker. Posterior sucker or Acetabulum is present on ventral side. Cystogenous cells is the characteristic feature. Fully mature cercaria make their way through the Birthpore of redia into the liver of the the snail.

8. 5. Metacercaria larva Similar to cercaria . Cyst is present around it. Tail absent. Two suckers present. Flame cells increased in number. Excretory bladder opens to outside by an aperture.

9. Larval forms of Taenia solium 1. Hexacanth larva. Micromeres of embryo develop into small Larva having six chitinous Hooks, called the Hexacanth. Rounded in structure. Also called onchosphere when surrounded by embryosphere. Two coverings outer shell & inner embryonic membrane. Develops into cysticercus larva.

10. 2. Cysticercus larva Lives in muscle of pig. Formed of fluid filled vesicle called bladder. Two layers : outer cuticle , inner germinal layer. Germinal layer forms invagination called Proscolex. The flesh of pig having bladder worms is known as Measly pork.