1. Platyhelminthes
Acoelomate Flatworms

2. Today’s Objective
TSW take notes on the phylum Platyhelminthes including economic importance, an overview of class characteristics, and ecological niches.

3. General Flatworm Characteristics
Acoelomate – no body cavity coelom- solid mesenchyme (mesoderm)
First phylum to show a definite cellular mesoderm
Bilaterally symmetrical
Triploblastic; 3 distinct tissue or germ layers
Dorsoventrally flattened

4. General Characteristics (cont.)
Respiration by diffusion
Digestive system extensively branched
One opening for feeding and waste removal
Lack an anus
Primitive kidneys – protonephridia with “FLAME CELLS”

5. General Charcterisitcs (cont.)
First evidence of cephalization primitive brain
Some have eyespots
Directional movement
No true respiratory system or circulatory system
Usually hermaphroditic

6. Class Turbellaria Free-living flatworms
Some freshwater (Planaria), marine, or terrestrial
Most move by circular and longitudinal muscles
Some move by using cilia (or cilia + mucus)

7. Turbellarian Feeding - Carnivorous
Wrap body around prey
Entangling with mucous
Ingest the whole prey or suck its juices through a hardened stylet (modified pharynx)
in many species the pharynx is completely eversible and can envelope the entire prey
there is no anus so ingestion and egestion are through the mouth

8. Turbellarian Reproduction
Sexual Reproduction
Most hermaphroditic
Both sex organs discharge gametes into a common chamber even though this is true- cross fertilization is the most common mode of reproduction
Some self fertilization can and does occur
Asexual Reproduction
Fragmentation and Regeneration

9. Dugesia

10. Class Monogenea Parasitic Flukes Only one host Most external parasites
Gyrodactylus
Polystoma
Can cause major economic losses to fisheries

11. Class Trematoda Digenetic Flukes
Complex life history, involves 2 or more hosts
Live in every type of environment
5,000+ known species
Live mostly in digestive system or associated organs (all parasitic)

12. Some Trematodes of Importance
Clonorchis – Chinese human liver fluke
Fasciola hepatica – Liver fluke
Schistosoma – Blood fluke
Know this life cycle!
Where they are present it is hazardous to bathe, drink, wade in or dip your arms in infested waters!

13. Class Cestoda - Tapeworms
Long, Flattened
White or Yellow in color
All parasitic!
Adults almost always live in the intestines of their hosts
Body has protective cuticle
Head (scolex) has multiple disks of hooks for attachment

14. Cestodes (cont.) Can reach up to 50 ft. in length!
No specialized sense organs
Reproduce using proglottids (segments)
Contain flame cells, nerves, muscles, male and female reproductive organs
Shed in feces of host
Taenia saginata – beef tapeworm
Taenia solium – pork tapeworm

15. Tapeworm Structure