Platyhelminthes

1. WORMS
•Platyhelminthes
•Nematodes
•Annelids
Annelids

2. WORMS
•Plathyhelminthes
•Nematodes
•Annelids
Annelids

3. Phylum Platyhelminthes
The Flatworms

5. Phylum Platyhelminthes
• About 20,000 species
» About 80% of parasites are from this phylum
• Divided into two major groups
• Free-living flatworms (Planaria)
• Parasitic (Tapeworm and fluke)
Planaria
Fluke
Tapeworm (Taenia)

6. Flatworms
• Thin and soft body divided in
segments but without locomotive
organs
• Range in size
– Some microscopic free-living
forms
– Parasitic forms over 20 meters
long
• Show many advances over Cnidaria

7. General Characteristics
– Bilateral symmetry
»the most
primitive
bilateral animals
– Development of definite
anterior and posterior
ends
– Tissue-organ level of
organization
– No locomotor organs
– Flattened body shape
»Dorso-ventrally
Planaria
Tapeworm (Taenia)
Fluke

8. Planaria
(class Turbellaria)
• Typical flatworms
• 5-25 mm in length
• Freshwater organisms
– Streams and ponds
– Beneath rocks, leaves,
logs, etc.
• Planaria are carnivores
– Smaller animals
– Dead organisms

9. Internal Structure of a Planarian
• Simple digestive system
– Mouth
• Pharynx – tube that can be extended through the mouth
– GVC
• With a primitive branched intestine

10. Reproduction in Planaria
• Asexual Reproduction
– Fragmentation. Head separates and forms tails.
– Unbelievable potential for regeneration!!
– Tails CAN regenerate heads!!

11. Reproduction in Planaria
• Sexual Reproduction
– Hermaphrodites . . . Again!
– REMEMBER: self-fertilization does not occur
– Fertilization is INTERNAL

12. Flukes and Tapeworms
• Specialized
adaptations for
parasitic lifestyle
– Thick cuticle to
protect against
digestive
enzymes
– Structures to
allow parasite to
attach to host
Liver Fluke
Tapeworm

13. Tapeworms
scolex
Suckers
Hooks

14. Taenia solium
Tapeworms

15. Specialized Reproductive
Measures
• Each square making up the
body is a reproductive sac
– > 100,000 fertilized eggs
– Each square will
eventually break off and
is released in the feces
of the host
» Proglottids
– Capsule surrounding
larva is digestable,
allowing the infection of
a new host
Proglottids

17. Platyhelminthes
Advances in Adaptation
• Symmetry
» Bilateral
• Cephalization
» Distinct anterior advancements
» Coordinated movement
• Asexual and Sexual Reproduction
» Regeneration
» Internal fertilization
» parasitism