Platyhelminthes General Characteristics, Classification and Examples | Free Biology Notes

Platyhelminthes General Characteristics

Platyhelminthes General Characteristics, Classification and Examples

After reading this article you will learn about Platyhelminthes General Characteristics and classification.

Platyhelminthes General Characteristics

  • Most are Parasitic on other animals and some are free living forms
  • They have dorsoventrally flattened body hence are called flat worms
  • Body is formed from three germinal layers
  • Locomotory organs are absent in these animals but adhesive organs like suckers, hook are present in parasitic form
  • On the body wall of parasitic animals a thick cuticle is present called tegument
  • These thick cuticle protects the parasite from the digestive enzymes of the host
  • Muscles in the body wall are mesodermal
  • Below the epidermis longitudinal, circular and oblique muscles are present
  • Digestive system incomplete or absent
  • Skeleton, respiration and circulatory system are absent
  • They respire through body surface and anaerobic respiration is found in parasite
  • Nervous system is ladder like, consist of a nerve ring and longitudinal nerve cords
  • Excretion occurs through specialized cells called flame cells or solenocytes
  • Some members possess high regeneration capacity
  • Sense organ are better developed in free living forms (Cephalization)
  • Asexual reproduction occurs by fragmentation in many freshwater flatworms
  • In sexual reproduction they are hermaphroditic meaning each individual produces eggs and sperm
  • Fertilization is internal and cross fertilization is predominant
  • Life cycle is indirect or complicated with one or many larvae

Classification of platyhelminthes

Class 1. Turbellaria

  • Freeliving in both fresh and marine water
  • Body is unsegmented & leaf like
  • Cilia on body surface
  • Suckers absent. Adhesive organs present
  • E.g. Planaria, Bipalium

Class 2. Trematoda

  • Endoparasites or ectoparasites
  • Body is unsegmented & leaf like
  • Cuticle present and no cilia
  • Sucker and some times hooks present
  • E.g. Liver Fluke, Schistostomata

Class 3. Cestoda

  • Endoparasites in alimentary canal of vertebrates
  • Body is segmented & ribbon like
  • Cuticle present and no cilia
  • Sucker and hooks present
  • E.g. Tapeworm, Echinococcus

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