1. Platyhelminthes: The Flatworms

2. Platyhelminthes: The Flatworms
What makes something a planarian (member of phylum platyhelminthes)?
Bilateral symmetry
cephalization
Single digestive opening (pharynx)
Respire via diffusion
Triploblastic body plan

3. Bilateral Symetry

4. Pharynx: Mouth on a tube
Cephalization
Pharynx
Mouth

5. Poor Flat-worm! No Anus! (single digestive opening)

6. Respiration: No Lungs… just diffusion
That’s why they’re flat! More surface area for diffusion

7. Platyhelminthes have 3 cell layers

8. Human Germ Layers Ectoderm : skin + nerve system
Endoderm : digestive & respiratory organs
Mesoderm : everything else (heart, kidneys, muscles, etc.)

9. Cell Layers Porifera Diploblast: Cnidaria Triploblast:
Platyhelminthes & other complex animals
Cell layers
No cell layers, no tissues… just sponge
Ectoderm (outer layer & tentacles, etc.)
Ectoderm (skin, nerves, phalynx, etc.)
Endoderm (inner digestive layer – the mouth and gut)
Endoderm (mouth and gut)
Mesoderm (all other organs: eyes, muscles, etc.)

10. Anatomy of a Flatworm

11. Types of Platyhelminthes
There are 3 groups of platyhelminthes
Planarians
Flukes
Tapeworms

12. Planarians: Free living nice guys
Predators. Usually aquatic

13. Flukes: Parasites with Multiple Hosts
Fluke are obligate pathogens.
They have complex life cycles which require infection of multiple hosts.

14. Tapeworms
Parasites.