🪸 Introduction

Phylum Platyhelminthes (Flatworms): Members of this phylum have dorso-ventrally flattened bodies, hence they are commonly called flatworms.

  • Parasitic Adaptations: In the parasitic forms, structures like hooks and suckers are present for attachment to the host. Some absorb nutrients directly from the host through their body surface.

  • Excretion & Osmoregulation: Specialized cells called flame cells (protonephridia) help in osmoregulation (regulating fluid balance) and excretion (removal of waste).

  • Nervous System: Consists of a ladder-like arrangement of nerve cords and ganglia.

  • Examples: Taenia (Tapeworm), Fasciola (Liver fluke), Planaria (free-living).

🧬 General Characteristics

  • Habitat: These are mostly endoparasites found in animals, including human beings. Some are free-living aquatic forms.
  • Symmetry: Flatworms are bilaterally symmetrical.
  • Germ Layers: They are triploblastic (possessing three germ layers: ectoderm, mesoderm, endoderm).
  • Coelom: They are acoelomates (lacking a true body cavity).
  • Level of Organisation: They exhibit the organ level of organisation.

🌊 Reproduction

  • Sexes are not separate; they are hermaphrodites (monoecious).
  • Fertilisation is internal.
  • Development occurs through many larval stages (indirect development).
  • Some members like Planaria possess high regeneration capacity.

💡 Questions and Answers

Q1. Which flatworm exhibits regeneration?

A1. Planaria — capable of regenerating entire body from small fragments.

Q2. What are flame cells? What is their function?**

A2. Flame cells (or protonephridia) are specialized excretory and osmoregulatory cells found in Platyhelminthes. They consist of a cell body with a tuft of cilia that 'flickers' like a flame, creating a current that draws waste fluids through filtration slits into tubules, eventually expelling them from the body. Their primary functions are osmoregulation (maintaining water balance) and excretion of metabolic wastes.

Q3. What level of organization, symmetry, germ layer type, and coelom type are found in Platyhelminthes?**

A3. Platyhelminthes exhibit:

  • Organ level of organisation.
  • Bilateral symmetry.
  • Triploblastic germ layer organisation (ectoderm, mesoderm, endoderm).
  • Acoelomate condition (lack a true body cavity).

Q4. What is regeneration? Give an example from Platyhelminthes.

A4. Regeneration is the ability of an organism to regrow lost or damaged body parts. Some organisms can even regenerate a whole new individual from a small body fragment. A prominent example within Platyhelminthes is Planaria (Dugesia), which possesses a remarkable capacity for regeneration.

Q5. Give examples of a free-living and a parasitic flatworm.**

A5.

  • Free-living: Planaria (Dugesia) - found in freshwater.
  • Parasitic: Taenia (Tapeworm) - endoparasite in human intestines; Fasciola (Liver fluke) - endoparasite in the bile ducts of sheep and other mammals.