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Classes of Platyhelminthes

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Platyhelminthes or flatworms are dorsoventrally flattened bilaterally symmetrical tripoblastic but acoelomate animals which have a blind sac body plan.There are about 13,000 species, most of which are parasitic, a few commensal or free living. The free living forms occur in both fresh water and marine habitats.

Phylum Platyhelminthes is divided into three classes

  1. Class: Trematoda
  2. Class: Turbellaria
  3. Class: Cestoda

Class: Trematoda

This class includes a group of parasites that infect various animals including man. Body is specialised for parasitic mode of life.

Example-Fasciola hepatica (Liver fluke), Schistoma (Blood fluke)

Liver fluke: Fasciola hepatica

Liver fluke: Fasciola hepatica

Blood Fluke: Schistosoma

Blood Fluke: Schistosoma

Fasciola hepatica (Liver fluke)

It is an endoparasite found commonly in the bile ducts of sheep, goats and cattle causing the disease liver rot. Liver fluke is a hermaphrodite and the life cycle is completed in two hosts, viz., a primary vertebrate host an intermediate host called the water snail Limnaea truncatula. Most of them are brilliantly coloured.


Schistoma are human parasites popularly known as blood flukes. The infections caused by them are generally known as Schistosomiasis. Intermediate host of schistosoma is snail. Three species of Scistoma(S.haematobium, mansoni, japonicum)are found to be pathogenic in man.

Class: Turbellaria

This class includes mostly free living flat worms. Most of them are aquatic and bottom dwellers, few are pelagic and some are terrestrial.

Examples-Planaria, Bipalium




It is a free living flat worm found in ponds and streams. It is about 2 cm in length. The animal is brightly colored and the color varies in the same species in different environments. The planarians show remarkable ability of regeneration. A small piece of the body grows to a full animal.

Class: Cestoda

This class includes tape worms which are the intestinal parasites of vertebrates.

Example-Taenia solium (pork tapeworm), Taenia saginata (beef tapeworm)

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Pork Tape Worm: Taenia solium

Pork Tape Worm: Taenia solium

Taenia solium (Pork tapeworm)

It is a human parasite. The intermediate host is pig. Incidences of tapeworm infection are common all over the world in places where pork is eaten without proper and adequate cooking.

Taenia saginata (Beef tapeworm)

It is also a human intestinal parasite but the intermediate host is the cattle. Infection occur mainly by taking improperly cooked beef.

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Richman Thomas on April 26, 2017:

Wow! Great work for a visual learner.


dishita on April 05, 2016:

nice one

Deena (author) from India on January 23, 2013:

Thank you very much for your visit and comment.

Without image the topic is incomplete , that's why I put it there.

Dianna Mendez on January 18, 2013:

Well, I find this interesting but it also makes me squirm seeing these worms. Great write up and learned something today.

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