• They have a dorso-ventrally flattened body therefore also known as flatworms.
  • Mostly endo-parasitic, found in animals including humans.
  • Specialised cells called flame cells help in osmoregulation and excretion.



Body Organisation:

    • Platyhelminthes are triploblastic organisms, meaning they have three germ layers: ectoderm, mesoderm, and endoderm.
    • They have bilateral symmetry, with a distinct head region and a tapering tail end.
    • Flatworms exhibit organ-level organisation with specialised organs and systems and are acoelomates.
    • They possess a simple central nervous system consisting of ganglia and nerve cords.


    • Platyhelminthes exhibit a variety of locomotion methods.
    • Most flatworms employ a muscular, undulating motion to glide over surfaces or swim in water.
    • Some flatworms use cilia or muscular appendages to crawl or burrow.


    • Platyhelminthes can reproduce both sexually and asexually.
    • Asexual reproduction occurs through regeneration, where a complete organism can regenerate from a fragment e.g. Planaria.
    • Sexual reproduction involves the presence of separate sexes (male and female).
    • Some flatworms are hermaphroditic, possessing both male and female reproductive organs.
    • Fertilisation is usually internal, with sperm transferred to the female reproductive organs.

Feeding Strategies:

    • Platyhelminthes exhibit diverse feeding strategies.
    • Some flatworms are free-living predators, capturing and ingesting small organisms.
    • Parasitic flatworms may have specialised structures (hooks and suckers) to attach to and feed on their hosts.
    • Flatworms can absorb nutrients directly through their body surface, as they have a high surface-to-volume ratio.
  • Examples:

Taenia (Tapeworm), Fasciola (Liver fluke), Planaria.