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SS1: BIOLOGY - 1ST TERM

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  1. Introduction to Biology | Week 1
    6 Topics
    |
    1 Quiz
  2. Recognizing Living Things | Week 2
    3 Topics
    |
    1 Quiz
  3. Organisation of Life | Week 3
    3 Topics
  4. Classification of Living Organisms | Week 4
    7 Topics
    |
    1 Quiz
  5. Kingdom Prokaryotae / Monera & Kingdom Protista | Week 5
    3 Topics
    |
    3 Quizzes
  6. Kingdom Fungi & Kingdom Plantae | Week 6
    9 Topics
    |
    2 Quizzes
  7. Kingdom Animalia I | Week 7
    6 Topics
    |
    1 Quiz
  8. Kingdom Animalia II | Week 8
    5 Topics
    |
    1 Quiz
  9. The Cell | Week 9
    3 Topics
    |
    1 Quiz
  10. The Cell Structure and Functions | Week 10
    4 Topics
    |
    1 Quiz
  11. The Cell and its Environment | Week 11
    4 Topics
    |
    1 Quiz
  12. Nutrition in Plants | Week 12
    4 Topics
    |
    1 Quiz



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Lesson 7, Topic 4
In Progress

Phylum Platyhelminthes
(Flat Worms)

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0% Complete
Phylum Platyhelminthes
Phylum Platyhelminthes.

Phylum Platyhelminthes are also known as flatworms and they include many free-living and parasitic life forms.

Characteristics of Phylum Platyhelminthes:

Below are important characteristics of Platyhelminthes:

1. They are multicellular flatworms with tissues, organs and organ systems including a nervous system with a simple brain.

2. They are triploblastic with three body layers (ectoderm, mesoderm and endoderm)

3. They do not have a body cavity (acoelomates.)

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4. Their body is dorsoventrally flattened.

5. They exhibit bilateral symmetry. Bilateral symmetry is the arrangement of body parts into left and right halves on either side of a central axis.

flatworm internal
Symmetry in Flatworm (Phylum Platyhelminthes).

6. They are mostly parasitic; Some have parasitic adaptations like hooks and suckers e.g. tapeworms, for attachment to the internal tissues of the host, such as intestines and blood vessels.

Tapeworm
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Diagrams of a Tapeworm.

7. Some are free-living in salt water and fresh water. 

8. Free-living forms have an incomplete digestive system with a mouth and no anus. Parasitic forms have no digestive system. 

Planaria
Planaria (free-living flatworm)

9. Some have tiny bristles called cilia that help them move

10. They reproduce sexually by fusion of gametes and asexually by regeneration.

11. They are hermaphrodites i.e. both male and female organs are present in the same body.

Interestingly, schistosomes (blood flukes) have evolved two sexes, in contrast to almost all other parasitic flatworms which are hermaphrodites.

12. Their life cycle is complicated with more than one larval stage.

13. They are economically important because they cause serious illness in plants and animals.

14. Examples of Phylum Platyhelminthes are;

  • Tape worm (Taenia sp)
  • Liver fluke (Fasciola hepatica)
  • Schistosoma haematobium (urinary blood fluke)
  • Planaria

Classification of Platyhelminthes:

The classification of Platyhelminthes includes:

  • Turbellaria e.g. Planaria
  • Trematoda e.g. Liver fluke
  • Cestoda e.g. Tapeworm
Fasciola hepatica
Liver Fluke (Fasciola hepatica.)

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