Phylum: Aschelminthes

The cross sections of the members of aschelminthes are circular, and hence are called round worms.

Habitat: Most of them are aquatic. They may be free-living or parasitic on plants and animals.


Ascaris (Roundworm) Wuchereria (Filaria worm) Ancylostoma (Hookworm).

Body plan: They have a tube-within-tube plan and organ-system level of body organization.

Symmetry: The animals are bilaterally symmetrical.

Germ layer: They are triploblastic and pseudocoelomate animals.

Body characteristics: The body ribbon-shaped, and is covered by a thick cuticle.


  • Respiratory and circulatory systems are absent.
  • Digestive system is well developed.
  • Alimentay canal has a mascular pharynx.
  • The excretory organ is the protonephridia.

Reproduction: The members are hermaphrodites. There is sexual dimorphism. Females are larger than males.

Embryo Development: Fertilization is internal, and the development can be direct or indirect.


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