Platyhelminthes
- 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.
Characteristics-
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.
Locomotion:
- 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.
Reproduction:
- 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.
