1. By: Natalie Williams, Sammy Keshavarz, Avi Dalal
Platyhelminthes
By: Natalie Williams, Sammy
Keshavarz, Avi Dalal

2. Introduction to Platyhelminthes
Bilateral Symmetry
Commonly called Flatworms because their bodies are thin between the dorsal (top side) and ventral (bottom side) surfaces
Include free living and parasitic species
Four classes: Turbellaria (mostly free-living flatworms), Monogenea (monogeneans), Trematoda( trematodes, or flukes), and Cestoda (tapeworms).
Sammy Keshavarz

3. Turbellarians Commonly called planarians
Inhabit unpolluted ponds and streams
Prey on smaller animals or feed on dead animals
Sammy Keshavarz

4. Cestoda Commonly called tapeworms Parasitic
The adults live mostly inside vertebrates, including humans
Large tapeworms can block the intestines and rob enough nutrients from the human host to cause nutritional deficiencies.
Sammy Keshavarz

5. Monogeneans and Trematodes
Live as parasites in or on other animals
Many have suckers for attaching to internal organs or to other outer surfaces of the host
Blood Flukes (Trematode) have infected 200 million people worldwide.
Sammy Keshavarz

6. Basic Anatomy
Natalie Williams

7. Body Cavity Platyhelminthes have no body cavity other than the gut
They lack an anus so the same pharyngeal opening takes in food and expels waste
Some tissues and organs exist but are not located in the body cavity.
Natalie Williams

8. Body Symmetry They are unsegmented, bilaterally symmetrical worms
Bilateral Symmetry- Only one imaginary cut divides the animal into mirror-image halves.
They are triploblastic which means they are composed of three fundamental cell layers.
Natalie Williams

9. Nervous System Have a cephalized nervous system
The head ganglion are usually attached to nerve cords connected by transverse branches across the body
Natalie Williams

10. Circulatory System
Platyhelminthes lack a circulatory or respiration system
Instead, they have absorption through the body wall
Natalie Williams

11. Digestive and Excretory System
A flatworm has a combination digestive/excretory system. It takes food in and gets rid of wastes through the same opening called the pharynx.
Digestive Juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastrovascular cavity, where digestion continues.
Digestion is completed within the cells lining the gastrovascular cavity, which has three branches, each with fine sub branches that provide an extensive surface area.
Gastrovascular Cavity- A sac with a central digestive compartment.
The fine branches of gastrovascular cavity distribute food throughout the animal.
Sammy Keshavarz

12. Locomotion/Musculature
A flatworm has no skeleton.
Contains three cell layers called the endoderm, the mesoderm and the ectoderm.
They move by using cilia (tiny bristles on the ventral surface) to glide along a film of mucus they secrete.
Sammy Keshavarz

13. Sensory Structures
A planarian’s head is equipped with a pair of light sensitive eyespots and lateral flaps that function mainly to detect specific chemicals.
The planarian’s nervous system can adapt and modify its responses depending on stimuli.
Ganglia, located at the anterior end of the worm, near the main sources of sensory input, are a pair of dense clusters of nerve cells.
Ventral nerve cords branch out through the rest of the body from the ganglia.
Avi Dalal

14. Reproduction (Methods/Types)
Planarians can reproduce asexually through regeneration.
Sexual reproduction is still possible.
Since planarians are hermaphrodites, sexual reproduction occurs through the exchange of sperm.
Avi Dalal

15. Gas Exchange Occurs through diffusion across the body surface.
Gas exchange is made easier because their flat shape places all cells close to the surrounding water.
No specialized organs for the function.
Their relatively simple excretory apparatus functions mainly to maintain osmotic balance with their surroundings.
Avi Dalal

16. Other Unique Features
Reproductive organs occupy nearly the entire interior of worms.
Can manipulate the hosts’ immune system into tolerating the parasite’s existence.
Sometimes have alternating sexual and asexual stages.
Some parasites can survive in humans for over 40 years.
Avi Dalal

17. Quiz!
1. All of the following classes of Platyhelminthes are parasitic EXCEPT:
Tapeworms
Monogeneans
Planarians
Trematodes
Sammy Keshavarz

18. Quiz!
1. ANSWER:
c) Planarians
Sammy Keshavarz

19. Quiz!
2. What are the main sources of sensory input in Platyhelminthes?
a) Gastrovascular cavity
b) Ventral Nerve Cords
c) Ganglia
d) Eyespots
Avi Dalal

20. Quiz!
2. ANSWER:
c) Ganglia
Avi Dalal

21. Quiz! 3. By which method do Planarians reproduce asexually? a) Mitosis
b) Meiosis
c) Regeneration
d) Conjugation
Avi Dalal

22. Quiz!
3. ANSWER:
c) Regeneration
Avi Dalal

23. Quiz!
4. Since Platyhelminthes lack a circulatory or respiratory system, how do they absorb those necessary nutrients?
a) They have a circulatory and respiration system
b) Absorption through the body wall
c) From bacteria that inhabit inside the organism
d) Absorption from food intake
Natalie Williams

24. b) Absorption through the body wall
Quiz!
4. ANSWER:
b) Absorption through the body wall
Natalie Williams