1. Phylum Platyhelminthes
Name? From 2 Greek words:
‘platy’ meaning flat and ‘helminth’ meaning worm
Characteristics:
Have tissues and internal organs
Have 3 embryonic germ layers – endoderm, mesoderm
and ectoderm
Bilateral symmetry
Cephalization
Acoelomates – No body cavity persent

3. 3 Main Groups or Classes:
Turbellaria – Free living, most live in marine or
Fresh water.
Example: Planaria (Fresh water)

4. Marine dwelling:

5. Some live on the forest floor:

6. 2. Class Trematoda (Flukes):
Parasitic flatworms often living in the host’s
internal organs.
Some are ectoparasites on the host’s skin, mouth, gills, etc.

7. Liver fluke in deer

8. 3. Class: Cestoda
Tapeworms – Long, flat parasitic worms
adapted to life inside the intestines of their hosts.

9. Characteristics: Have tissues and internal organs
Have 3 embryonic germ layers – endoderm, mesoderm
and ectoderm
Bilateral symmetry
Cephalization
Acoelomates – No body cavity persent

10. Specialized structures:
Free living flatworms: Ganglia (groups of nerve cells)
that control a nervous system – primitive ‘brain’.
Also have eyespots to
detect light with

11. Free living flatworms have mouth with a pharynx
that pumps food into the digestive cavity.

12. Free living flatworms have muscle cells to aid in
movement
Some flatworms have flame cells that help them remove
excess water and also wastes like ammonia and urea
from the body. (Help with excretion)

13. Parasitic worms such as tapeworm:
Head (scolex) contains several hooks or suckers
that are used to attach to the intestinal wall of the host

14. Mode of nutrition:
Free living flatworms: Predators or scavengers – eat
molluscs, protozoans, crustaceans, some live with
algae that provide them with carbohydrates.
Use pharynx to pump in food into the mouth.
Have a digestive cavity or gut.
Parasitic flatworms: Feed on blood, tissue or pieces
of cells within the host’s body. Tapeworms have
no digestive cavity – simply absorb nutrients that
Are already in the host’s intestines.

15. Movement:
Free-living: Use cilia and muscle cells to glide, twist
and turn.
Reproduction:
Free living: Hermaphrodites and reproduce sexually.
Sperm are delivered between 2 flatworms. Eggs are
laid and hatch in a few weeks.
Also reproduce asexually through fission.

17. Parasitic flatworms:
They have complicated life cycles that can involve
both sexual and asexual reproduction.