Phylum : Platyhelminthes

The members of this phylum have dorso-ventrally flattened body and are hence called flatworms. The body has usually ribbon-like or leaf-like appearance.

Habitat: They live as endoparasites inside the body of animals including humans.

Examples:

Taenia (Tapeworm) Fasciola (Liver fluke) Planaria.

Body plan: Flatworms are acoelomate animals with blind sac body plan and organ level of organization.

Symmetry: The flatworms are bilateral symmetry.

Germ layer: They are triploblastic organisms.

Body characteristics: Parasitic forms have thick cuticle, suckers and hooks. Free living forms have a ciliated epidermis.

           

Physiology:

  • Respiratory and circulatory systems are absent.
  • Excretory cells are called flame cells. These are also involved in osmoregulation.

Reproduction: They are hermaphrodites and reproduction occurs by sexual means. But cross- fertilization also occurs frequently. Some members (like Planaria) have great powers for regeneration.

Embryo Development: Fertilization is internal. The development is indirect with many larval stages.

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