Animal Kingdom
NCERT Class 11 Biology | CBSE | NEET-UG Preparation
Study the basis of animal classification, the major non-chordate phyla, chordate characteristics and vertebrate classes. Revise important definitions, identifying features, examples and comparisons for CBSE examinations and NEET-UG.
Platyhelminthes and Aschelminthes
Phylum Platyhelminthes
Platyhelminthes are commonly called flatworms. Many are parasitic, while some, such as Planaria, are free-living.
- They are bilaterally symmetrical and triploblastic.
- The body is dorsoventrally flattened.
- They show organ-level organisation.
- They are acoelomates.
- Flame cells assist excretion and osmoregulation.
- Many parasitic forms possess hooks and suckers.
- Many members are hermaphrodites.
Examples: Planaria, Taenia and Fasciola.
Phylum Aschelminthes
Aschelminthes are commonly called roundworms. They may be free-living or parasitic.
- They are bilaterally symmetrical and triploblastic.
- The body is cylindrical and unsegmented.
- They are pseudocoelomates.
- The alimentary canal is complete, with separate mouth and anus.
- Sexes are generally separate, and sexual dimorphism may occur.
Examples: Ascaris, Wuchereria and Ancylostoma.
| Feature | Platyhelminthes | Aschelminthes |
|---|---|---|
| Common name | Flatworms | Roundworms |
| Body shape | Dorsoventrally flattened | Cylindrical |
| Body cavity | Acoelomate | Pseudocoelomate |
| Alimentary canal | Usually incomplete; absent in some parasitic forms | Complete |
| Example | Taenia | Ascaris |
NEET focus: Flame cells are associated with Platyhelminthes. A complete alimentary canal and pseudocoelom are characteristic of Aschelminthes in the traditional NCERT classification.
