1. Phylum Platyhelminthes
Flatworms

3. Unsegmented worms Simplest animals with Bilateral symmetry
Characteristics
Unsegmented worms
Simplest animals with
Bilateral symmetry

4. No specialized circulatory or respiratory system
(uses diffusion to transport oxygen and nutrients)
Excretes by diffusion

5. Cephalization (sense organs and nerve cells gathered into a head region)
Primitive organ systems with true organs (digestion, excretion)

6. Sexual and asexual reproduction (hermaphroditic but don’t self fertilize)
Free-living and parasitic
mobile

7. Free-Living Flatworms (Aquatic) eg. Planaria

8. Planaria – cross-eyed fresh water worm

9. Free-living Flatworms PLANARIA
Both marine and freshwater
Most are small
(less than cm and few mm thick)

10. Primitive nervous system allows for coordination of body movements
Simple eyes that detect light changes (respond to stimuli!!)

11. Locomotion: cilia help glide through water, muscles allow them to twist and turn
Feeding : Some are carnivores , others are scavangers.
Gastrovascular cavity with one opening at the end of the muscular tube called a pharynx.(used to suck food in to gastrovascular cavity)
Gastrovascular cavity-intestine with many braches.
Intestine secrete enzyme to help break down food.
Digested food can diffuse from the intestine into nearby cells.

12. Reproduction
Sexual – one worm delivers sperm, while other receives, egg laid in clusters
Asexual by fission

13. Parasitic Flatworms (Flukes) eg. Tapeworms

15. Parasitic Flatworms TAPEWORMS!!
Scolex
Proglottids (sections) form at anterior end

16. Found inside and outside hosts
If inside cannot afford to grow too large or it will kill its host.
Tapeworm: Have a scolex (head) with several suckers and ring hooks ---attach to intestinal wall.
Some can reach up to 30 m in length (found in a sperm whale) Human tapeworms can be 7 m

17. Live in intestines - Feed on blood, tissue, fluids and pieces of cells
Lack : sensory organs, coordination for mobility, digestive system

18. Highly developed reproductive system capable of producing hundreds and thousands of egg and sperm.
No digestive tract – absorb food as it passed by

19. developed a way to maximize absorption of nutrients from their host
being flat
VERY long
(which increases their surface area to maximize the absorption of nutrients)

20. Schistosoma mansoni Life cycle: Swimming larvae Burrow into snail
Reproduce asexually
Break out of snail
Swim in water
Bores through skin of human to blood vessels and then intestines
Blood vessels leak eggs into intestines
Very sick human

21. Tapeworm life cycle
Mature proglottids break off posterior
Eggs are released
Animal eats contamination
Forms a dormant cyst
Human eats
Hatch in host