Platyhelminthes General Characteristics, Classification and Examples | Free Biology Notes

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