Platyhelminthes are a phylum of flatworms that are acoelomate and bilaterally symmetrical. They may be free-living or parasitic. The phylum contains three classes: Turbellaria, which are free-living flatworms found in freshwater; Trematoda, which are parasitic flukes that have complicated life cycles and infect mollusks and vertebrates; and Cestoda, which are tapeworms that are exclusively parasitic and segmented, lacking digestive systems but containing reproductive organs in each segment. Examples of classes and organisms discussed include the free-living planarian, the liver fluke Fasciola that infects sheep, and the pork tapeworm Taenia

1. PHYLUM PLATYHELMINTHES- REPRESENTATIVES
LECTURE-05
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2. Platyhelminthes- General Characteristics
• They are triploblastic, acoelomate, and bilaterally symmetrical.
• They may be free-living or parasites.
• The body has a soft covering with or without cilia.
• Their body is dorsoventrally flattened without any segments and appears like a leaf.
• They are devoid of the anus and circulatory system but has a mouth.
• They respire by simple diffusion through the body surface.
• They have an organ system level of organization.
• They do not have a digestive tract.
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Platyhelminthes body plan

4. General Characteristics
• They are hermaphrodites, i.e., both male and female organs are present in the same
body.
• They reproduce sexually by fusion of gametes and asexually by regeneration by
fission and regeneration.
• Fertilization is internal.
• The life cycle is complicated with one or more larval stages.
• They possess the quality of regeneration.
• The flame cells help in excretion and osmoregulation.
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5. Unique Characters
• Presence of flame cells.
• Ladder-like nervous system.
• Presence of parenchyma in the body cavity.
• Self-fertilization
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6. Classification
Classification
Class Turbellaria Class Trematoda Class Cestoda
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7. A. Class Turbellaria
• These are free-living organisms found mostly in fresh water.
• The body is dorsoventrally flattened.
• Hooks and suckers are not present.
• True bilateral symmetry.
• Unsegmented.
• Ciliated epidermis.
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8. A. Turbellaria
• Parenchyma between the epidermis and the gastrodermis.
• Some cephalization.
• Blind ending gut.
• Flame cells for excretion.
• For example; Planaria, Otoplana
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9. Example: Dugesia (Planaria)
• These are found in freshwater ponds or slow streams.
• Their body possesses cilia and has the power of regenerating the lost part.
• The head bears a pair of eyes and two lateral lobes.
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10. Reasons of identification-Planaria
• The planarian has a soft, flat, wedge-shaped body that may be black, brown, blue,
gray, or white.
• The blunt, triangular head has two ocelli (eyespots)
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11. Planarian Morphology
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12. B. Class Trematoda
• These are mostly parasitic.
• they have several hold fast devices present (opisthaptor)
• they have complicated life cycles involving sexual and asexual reproduction
• they are digenetic flukes
• Hooks and suckers are usually present.
They have 2 hosts; the intermediate host is a snail while the definitive host is a
vertebrate
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13. B. Trematoda
Tegument- the outer layer of the epidermis which forms a syncytium and is highly
effective at providing protection and absorbing nutrients
Scyncytium - a continuous layer of fused cells
about 10000 species
Examples in Humans:
Sheep Liver Fluke (Fasciola hepatica)
Schistosomes (Dioecious Blood Fluke)
Chinese Liver Fluke (Clonorchis sinensis)
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14. A; Diplozoon
B; Fasciola hepatica,
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15. Schistosomes (Dioecious Blood Fluke)
• Schistosoma is a genus of trematodes, commonly known as blood flukes
• It is found in the mesenteric blood vessels and hepatic portal system of humans
and is therefore known as blood fluke.
• It shows well-marked sexual dimorphism.
• Schistosoma causes Schistosomiasis which spreads through contaminated water.
• The patient suffers from anaemia, pain, fever, liver and spleen enlargement, and
diarrhoea.
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16. Schistosomes (Dioecious Blood Fluke)
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17. Example: Fasciola spp.
It is also known as liver fluke since it resides in the liver and bile duct of sheep and
goat.
It is a hermaphrodite but cross-fertilization takes place.
It causes fascioliasis in animals.
In this, the liver of the animal enlarges and the bile ducts are blocked.
The infection weakens the muscles of the animals resulting in muscular pain.
It might also prove fatal for the animals.
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18. Sheep Liver Fluke (Fasciola hepatica)
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19. Examples of Fasciola Spp.
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20. C. Class Cestoda
• Cestodes oftentimes called as tapeworms, It's because their bodies have a tape-
like, segmented shape to it.
• These are exclusively parasitic.
• Lack a digestive system.
• They have hooks and suckers.
• Each proglottid contains a set of reproductive organs.
• For example; Taenia spp., Convoluta
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21. Cestodes-Examples
• There are other organisms such as Taenia saginata that is transferred through beef in
the human intestines,
• Echinococcus granulosus that lives in the intestine of cats and dogs.
Taenia saginata
Echinococcus granulosus
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22. Examples: Taenia solium
• It is also known as the pork tapeworm and is found in all the countries where pork is
consumed.
• They live as parasites in the small intestine of human beings and their larva are found
in the muscles of the pigs.
• It is a hermaphrodite and undergoes self-fertilization.
• Taenia solium causes taeniasis where the patient experiences abdominal pain, anaemia,
indigestion, restlessness and false appetite.
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23. Tapeworm-Morphology
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24. Tapeworm-Reasons of identification
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Tapeworms are bilaterally symmetrical.
Presence of a series of identical segments called proglottids.
Presence of head, or scolex that bears suckers and often hooks.

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