1. Phylum Platyhelminthes The Flatworms

2. Phylum Platyhelminthes About 20,000 species »About 80% of parasites are from this phylum Divided into three major groups Free-living flatworms Parasitic tapeworms Parasitic flukes

3. Flatworms Range in size –Some microscopic free-living forms –Parasitic forms over 20 meters long Show many advances over Cnidaria

4. General Characteristics The following characteristics are shared by ALL flatworms: –Bilateral symmetry »the most primitive bilateral animals –Development of definite anterior and posterior ends –Tissue-organ level of organization »Simple organ systems –Flattened body shape »Dorso- ventrally

5. Body Plan of Flatworms Acoelomate –No Body cavity NOT a tube-within-a-tube –One simple tube GVC present Incomplete digestive tract –One opening –Food and wastes enter / exit through same opening »Two way flow

6. 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

7. Internal Structure of a Planarian Simple digestive system –Mouth Pharynx – tube that can be extended through the mouth –GVC With a primitive branched intestine Extracellular and intracellular digestion (cells lining intestine)

8. Getting Around … Movement Towards Cephalization Planaria can move about freely –Muscles –Underside covered with cilia Presence of eyespots –Small brain located beneath Development of primitive nervous system –Two nerve cords extend the length of the body –Transverse nerve cords extend across the body

9. Reproduction in Planaria Asexual Reproduction –Fission »Head separates from tail end –Unbelievable potential for regeneration!! –Tails CAN regenerate heads!!

10. Reproduction in Planaria Sexual Reproduction –Hermaphrodites... Again! –REMEMBER: self-fertilization does not occur –Fertilization is INTERNAL –Fertilized eggs are shed in protective capsules –Eggs hatch into tiny new planarians!

11. What’s Different About 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

12. Tapeworms scolex Suckers Hooks

13. 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

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

15. Platyhelminthes fact: The longest flatworm ever found, a tapeworm, was over 90 FEET LONG...