1. Platyhelminthes The Flatworms
Pechenik: 34,000 spp (Brusca & Brusca: 20,000 spp)
Characteristics:
Triploblastic
Ectoderm, mesoderm, endoderm
Acoelomate
Bilateral symmetry (w some cephalization)
Protonephridia = Organs for excretion/osmoregulation
Flatness allows diffusion for gas exchange
80% are parasitic
Simultaneous hermaphrodites (monoecious)

2. Phylum Platyhelminthes
Opisthaptor
Ectoparasite
One host
Trematoda
Acetabulum
endoparasite
Mollusc/vertebrate
life cycle
Cestoda
Monogenea
Turbellaria
Free living
Microtriches
Scolex
Proglottids
Cilia lost from ectoderm
(parasitic lifestyle)
Phylum Platyhelminthes

3. Class Turbellaria

4. Class Turbellaria

5. Class Turbellaria

6. Class Turbellaria

7. Class Turbellaria

8. Class Turbellaria Most are free living Marine & FW Sensory receptors
Chemical (auricles)
Tactile
Light
Dugesia sp.

9. Class Turbellaria Most are free living Marine & FW Sensory receptors
Chemical
Tactile
Light
Cephalized
Crawl on substrate using cilia
Dugesia sp.

10. Class Turbellaria
Incomplete digestive tract
Pharynx

11. Class Monogenea
haptor
opisthaptor

12. Class Monogenea
Ectoparasites of fish skin and gills
Only 1 host

13. Monogenea Reproduction: Eggs → oncomiracidium larva → attach to fish
Larva similar to cestode oncosphere
Adults resemble digene trematoda (convergent evolution – life cycles very different)