1. Platy = flat Helminth = worm
Platyhelminthes
Platy = flat
Helminth = worm

2. Taxonomy Phylum Platyhelminthes
Kingdom Animalia
Phylum Platyhelminthes
Class Turbellaria Class Trematoda Class Cestoda
(planarians) (flukes) (tapeworm)

3. Platy = flat
Helminth = worm
Flatworms
flatworm biology

9. General Characteristics
Body is flattened dorsoventrally (from back to belly)
Acoelomates: have no true body cavity
Most are parasitic but a few are free-living
Three body layers: ectoderm, mesoderm, endoderm
Cephalization: sensory organs are clustered a head region
Simplest animals with bilateral symmetry

10. Body Plan Three body layers Digestive cavity Bilateral symmetry
Acoelomates
Have only 1 body opening- no anus

11. Digestion 2-way digestive tract
Free-living: food enters through the mouth and pharynx
Parasitic: suckers take in predigested food – no digestion is needed

12. Circulation and Respiration
No circulatory system
Gases diffuse through skin
FLAME CELLS: cells that circulate water and nutrients

13. Sensory organs Eyespots (in some) Ganglia (bundles of nerves)
Nerve cords

14. Movement
Secrete mucus and use cilia on their ectoderm layer to glide along surfaces
Use muscle contractions to twist and turn
flatworm moving

15. Reproduction
All are hermaphrodites that do NOT fertilize their own eggs (except tapeworms)
All can reproduce sexually as well
Asexual: budding, fission, regeneration
Sexual: monoecious but don’t fertilize their own eggs

17. Ecological Importance
Most are parasitic (Endoparasites)
Free-living forms live in water and are a food source for many other animals

18. Class Turbellaria Planarians and marine flatworms All are free-living
Live in all water environments (lakes, ponds, oceans etc.)
Planarians
worlds weirdest

19. Class Trematoda Flukes All are parasitic Found in warm, tropical areas
Can make people extremely sick or even cause death
snail parasites
blood flukes

21. Intestinal fluke

22. Liver Fluke

23. Class Cestoda Tapeworms All are endoparasites
Live in the intestines of mammals
Has a scolex and hooks to attach to the host
Contracted by eating undercooked meat
tapeworms
tapeworm2
tyrabanks
human parasites

25. Videos parasites in fish parasite in eye Platyhelminthes
mind controlling parasites