SS1: BIOLOGY - 1ST TERM
Introduction to Biology | Week 16 Topics|1 Quiz
Recognizing Living Things | Week 23 Topics|1 Quiz
Organisation of Life | Week 33 Topics
Classification of Living Organisms | Week 47 Topics|1 Quiz
Kingdom Prokaryotae / Monera & Kingdom Protista | Week 53 Topics|3 Quizzes
Kingdom Fungi & Kingdom Plantae | Week 69 Topics|2 Quizzes
Kingdom Animalia I | Week 76 Topics|1 Quiz
Kingdom Animalia II | Week 85 Topics|1 Quiz
The Cell | Week 93 Topics|1 Quiz
The Cell Structure and Functions | Week 104 Topics|1 Quiz
The Cell and its Environment | Week 114 Topics|1 Quiz
Nutrition in Plants | Week 124 Topics|1 Quiz
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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.)
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.
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.
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.
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)
Classification of Platyhelminthes:
The classification of Platyhelminthes includes:
- Turbellaria e.g. Planaria
- Trematoda e.g. Liver fluke
- Cestoda e.g. Tapeworm