1. Phylum Platyhelminthes

2. Goals for today
Learn to recognized the Phylum Platyhelminthes from other animals
Learn the main ‘diagnostic’ characteristics
Learn about some free-living and parasitic species biology

3. Phylum Platyhelminthes: flatworms
These are acoelomate metazoans
Porifera
Parazoa
Deuterostomia
Ecdysozoa
Annelida
Mollusca
Lophophorata
Rotifera
Platyhelminthes
Lophotrochozoa
Eumetazoa
Bilateria
Radiata
Protostomia
Cnidaria and Ctenophora
More organized than radiate animals in that:
Bilateral symmetry
Third germ layer-mesoderm (triploblastic animals)
Excretory system made up of specialized flame cells and tubules for removal of nitrogenous waste
Highly organized nervous system and sense organs in the anterior part of the body (cephalization)

4. Phylum Platyhelminthes: Classification
Classes:
Turbellaria:
Ciliated epidermis
Paraphyletic group
Mostly free-living
Cestoda:
Syncytial tegument without cilia
Long ribbon like body shape
Body divided in proglotids
Organs to attach host in the oral part of the body: suckers, hooks
No digestive system
Parasitic in digestive tract of all classes of vertebrates
Trematoda:
Digenetic flukes (having two stages of multiplication, one sexual in the mature forms, the other asexual in the larval stages)
Syncytial (many nuclei within a single cell) tegument without cilia
Leaf-like to cylindrical shape.
Organs to attach host in the oral and ventral part of the body: suckers, NO hooks
Parasitic in all classes of vertebrates

5. Phylum Platyhelminthes: Your Tasks
Class Turbellaria
Genus: Dugesia
Planarias are freshwater usually under stones or submerged leaves or sticks. But other members of the class are marine

6. Phylum Platyhelminthes: Dugesia
1. Take a slide from your box with a planaria: identify the eyespot, aurículas, intestino, faringe, y boca.
intestino
boca
What is the function of the eyespot and the auricles? ____________
Check your book for answers!

7. Phylum Platyhelminthes: Dugesia
As in cnidarians the digestive tract of turbellarians is a gastrovascular cavity, the branches of which fill most of the body.
They don’t have an anus so undigested food is ejected through the mouth! Yikes 

8. Phylum Platyhelminthes: Dugesia
Reproduction: these animals are monoecious (hermaphrodites) they can reproduce sexually and asexually by transverse fission
Asexual reproduction, the planarian detaches its tail end and each half regrows the lost parts by regeneration, allowing neoblasts (adult stem cells) to divide and differentiate.
sexual reproduction
Planarians exchange sperm.
Eggs develop inside the body and are shed in capsules. Weeks later, the eggs hatch and grow into adults.
Sex is desirable because it enhances the survival of the species by maintaining the level of genetic diversity.

9. Phylum Platyhelminthes: Dugesia
Excretion and osmorregulation: the excretory system consist of canals and protonephridia called flamed cells.

10. Phylum Platyhelminthes: Dugesia
2. Take a slide from your box with a planaria cross section cuts: identify intestino, diverticulos intestinal, lumen de la faringe, musculos dorsoventrales.

11. Planaria – cross section
circular muscle
rhabdites
longitudinal muscle
epidermis
intestine
mesenchyme
lumen of pharynx
pharyngeal pouch
pharynx

12. Phylum Platyhelminthes: Dugesia
3. Observe live planarias. Take a look to their locomotion. How does it use the head and auricles? Does it ever move backwards?

13. Phylum Platyhelminthes: Dugesia
4. Observe live planarias. Perform with your instructor the stimuli experiments described in page 136.
Response to touch
Response to food
Response to directional illumination
Write your answers this is part of the Planaria report

14. Phylum Platyhelminthes: Dugesia
5. Regeneration :
Some planarians exhibit an extraordinary ability to regenerate lost body parts.
A planarian split lengthwise or crosswise will regenerate into two separate individuals
When divided in two it will first regrow the head.
Body segment differ in capacity to regenerate, because the amount of neoblasts differs in the area around the cut.

15. Phylum Platyhelminthes: Your Tasks
Class Trematoda
Genus: Clonorchis sinensis
Clonorchis lives in the human bile duct (bilis) where it feeds on bile and lacerated cells from the inflamed bile duct very common in Asia

16. Phylum Platyhelminthes: Clonorchis
1. Observe slide of Clonorchis sinensis: identificar ventosa oral, boca, faringe, intestino, ventosa ventral, glandula de yema, poro genital, vesicula semina, ovario, receptabulo seminal, testículos, vejiga, poro excretor

17. Phylum Platyhelminthes: Your Tasks
Class Trematoda
Genus: Schistosoma mansoni
Schistosoma are blood flukes of humans that affect ~ 200 million people in Asia, Africa, the Caribbean (including Puerto Rico!) and South America.
Disease: Schistosomiasis

18. Phylum Platyhelminthes: Schistosoma
1. Ciclo de vida: Observe slides of Schistosoma mansoni adults, eggs, and cercariae
eggs
miracidum
cercariae
You need to understand the life cycle
adults

19. Phylum Platyhelminthes: Your Tasks
Class Cestoda
Genus: Taenia pisiformis- dog tapeworm
Extreme parasites:
No digestive system.
Tegument specialized epidermis that absorbs nutrients and rejects toxins and digestive enzymes.
Live is all about maximize reproduction. In fact tapeworms are egg factories, some species can even fertilize their own to guarantees offspring.
No son segmentos

20. Phylum Platyhelminthes: Taenia
1. Observe slide of Taenia. Noticed the scolex and the body composed of units called proglottids which are not segments, but units formed by budding behind the scolex.
Scolex
proglottids

21. Phylum Platyhelminthes: Taenia
1. Observe slide and model of Taenia scolex which is equipped with suckers and hooks. Note the neck from which new proglotids are budded off.
A= suckers
B=hooks
scolex

22. Phylum Platyhelminthes: Taenia
2. Observe slide and model of Taenia mature proglotid. They have reproductive organs: testículos, vaso deferente, poro genital, glandula de yema, ovario, vagina, utero, cordon nervioso, canales excretores.

23. Uterus

24. Phylum Platyhelminthes: Taenia
2. Observe slide and model of of Taenia gravid proglottid, with the uterus fulled with eggs or embryos. Where do you find gravid proglottids? These proglottids break off and shed in the feces of the host. Outside the host the proglottid breaks releasing thousands of infected eggs.
Uterus with eggs

26. Phylum Platyhelminthes: Taenia
Taenia life cycle

27. Important Links Platyhelminthes