1. FLATWORMS
Kingdom Animalia
Phylum Platyhelminthes
Ex. Planaria, flukes and tapeworms
Class Cestoda
Class Turbellaria
Class Trematoda

2. Characteristics of Platyhelminthes
• Body symmetery: bilateral
• Body organization: triploblastic (3 layers)
– Ectoderm
– Mesoderm (first!!)
– Endoderm
• Body Cavity: acoelomate

4. Characteristics continued
• Digestive system:
mouth &
gastrovascular cavity
• Reproduction:
– Sexual:
hermaphroditic –
cross fertilization
occurs between 2
worms
– Asexual:
fragmentation

5. Characteristics continued:
• Circulation: diffusion
• Nervous system:
– Cephalization (first) &
nerves
– Eyespots, auricles,
sensitive to light &
chemicals
• Respiration: diffusion
through skin
• Excretion: tubes open to
outside, flame cells (rid
of excess H2O)& mouth
• Habitat: host (intestine)
& freshwater

7. • Ecological roles:
– Parasitic
– Food source
– Eat dead animals
• saprophytes

8. Additional information:
Free living
ex) Planaria – freshwater
 Stores food as fat
 Brain coordinates
movement & capable
of learning its way
through a maze
 Able to respond to
light & chemicals

9. Additional information:
Parasitic
Ex) flukes and tapeworms
• Lives in digestive tract
& absorbs digested
food from host so, NO
digestive tract!
• This leaves more room
for reproduction –
capable of producing
1,000s of eggs.

10. Platyhelminthes vs Cnidarians
• Tissues organized into
organs
– Reproductive system
(organized organs)
• Three embryonic tissue
layers
– Mesoderm
• Bilateral Symmetry
• Cephalization and
nerve cords
• No true organs
• Two Tissue layers
• Radial Symmetry
• Nerve Net
**DO NOT COPY

11. Class Cestoda
• AKA tapeworms
• Tapeworms are parasites that live in the
digestive system of vertebrate animals

12. More on Tapeworms…
• Specialized for living within a host
– Lost most body systems
• No digestive, nervous, excretory, muscle systems
• Absorb food by diffusion through skin
– Has specialized reproduction

13. Tapeworm Reproduction
• Specialized body sections called proglottids
– Hermaphroditic
• Contain both ovaries and testes
• Can fertilize their own eggs
– Zygotes are passed out of host’s body with feces
– Larvae hatch in water and in grass
• Eaten by herbivore (intermediate host) – larvae then
burrows through wall of intestine and into blood stream
• Intermediate host contains tapeworm cysts (bladder
worm)– when ingested by final host (e.g. human) cyst
hatches out as scolex which then grows proglottids
**DO NOT COPY**

14. Tapeworm cont’d
• Two body regions
– Scolex – “head”
• No cephalization
• Hooks and suckers used to attach to inside wall of
intestine
– Proglottids
• Body segments for reproduction

18. Tapeworm life cycle

19. Fun Facts About Tapeworms
• Some tapeworms grow quite long. One species that
parasitizes horses has been known to attain a length of
75 feet.
• Ingesting tape worms for reducing weight is a diet
routine: A rather surprising fact about tape worms is that
ingesting them as a weight-loss technique is happening
even in these modern times. The person undergoing this
method has the direct risk of an infection. It also causes
a dramatic reduction in the body’s ability to absorb
nutrients; and a counter-effect, where the person eats
more to balance the metabolic stress once the diet
regime is over.
**DO NOT COPY**

20. Class Trematoda
Ex: Chinese liver fluke

21. Fluke (liver, lung, heart, intestine)
• Parasitic
– Pharynx swallows host’s tissue and body
fluids (including blood)
– Common intermediate host: raw fish
• No need for circulation or respiratory
system
– Live in tissues supplied by host’s blood
– Absorb through gastrovascular cavity
• Flame cells
• Nerve cords and anterior ganglia
– Do not have as specialized nerve cells like
Planaria
• Hermaphrodites
– Complex life cycle with numerous larval
stages that infect a number of hosts.

22. Liver Fluke Life Cycle

23. Blood Flukes

24. liver fluke

25. Class Turbellaria

26. Planaria
• Excretion
– Two networks of tubes
– Attached to tubes are flame cells
• Modified to work like a kidney
• Have cilia that cause excess
body fluid to move along
excretory tubes and eventually
out of planaria body
• Muscles
– Three layers of muscles below
ectoderm
– Constrict – shorten, and flatten
worm.

27. Flame Cell
1. Cell Nucleus
2. Bundle of Cilia (flame)
3. Parenchyma Tissue
4. Collecting Duct

29. 1. Pharynx
2. Auricle
3. Eye spot
4. Pharynx
5. Gastrovascular
cavity

30. Marine Flatworms

31. Flatworms are hermaphrodites
When flatworms encounter each other, they engage in a
60 minute ‘dance’ during which they repeatedly strike at
each other, both trying to inject their sperm under the skin
of the other worm.
The ‘winner’ becomes the male for that encounter, and
the ‘loser’ must become the female & care for the
fertilized eggs!
https://www.youtube.com/watch?v=wn3xluIRh1Y