Phylum Platyhelminthes
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
Phylum Platyhelminthes: flatworms
These are acoelomate metazoans
Parazoa
Lophotrochozoa
Protostomia
Radiata
Bilateria
Eumetazoa
Deuterostomia
Ecdysozoa
Annelida
Mollusca
Lophophorata
Rotifera
Platyhelminthes
– 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)
Cnidaria and Ctenophora
More organized than radiate animals in
that:
Porifera
Lophotrochozoa
Phylum Platyhelminthes:
Classification
Classes:
Turbellaria:
• Ciliated epidermis
• Paraphyletic group
• Mostly free-living
Cestoda:
• Syncytial tegument without
cilia
• Long ribbon like body shape
Trematoda:
• Body divided in proglotids
• Digenetic flukes (having two stages of
multiplication, one sexual in the mature forms, the • Organs to attach host in the
oral part of the body: suckers,
other asexual in the larval stages)
hooks
• Syncytial (many nuclei within a single cell)
• No digestive system
tegument without cilia
• Parasitic in digestive tract of
• Leaf-like to cylindrical shape.
all classes of vertebrates
• Organs to attach host in the oral and ventral part
of the body: suckers, NO hooks
• Parasitic in all classes of vertebrates
Phylum Platyhelminthes: Your Tasks
Phylum: Platyhelminthes
– Class Turbellaria
• Genus: Dugesia
Planarias are freshwater usually
under stones or submerged leaves
or sticks. But other members of the
class are marine
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!
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 
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.
Phylum Platyhelminthes: Dugesia
Excretion and osmorregulation: the excretory system
consist of canals and protonephridia called flamed
cells.
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.
Planaria – cross section
circular muscle
rhabdites
longitudinal muscle
epidermis
intestine
mesenchyme
pharyngeal pouch
lumen of pharynx
pharynx
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?
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
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.
Phylum Platyhelminthes: Your Tasks
Phylum: Platyhelminthes
– 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
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
Phylum Platyhelminthes: Your Tasks
Phylum: Platyhelminthes
– 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
Phylum Platyhelminthes: Schistosoma
1. Ciclo de vida: Observe slides of Schistosoma
mansoni adults, eggs, and cercariae
eggs
adults
miracidum
cercariae
You need to understand the life cycle
Phylum Platyhelminthes: Your Tasks
Phylum: Platyhelminthes
– 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.
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.
proglottids
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
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.
Uterus
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
Phylum Platyhelminthes: Taenia
Taenia life cycle
Important Links
Platyhelminthes
http://www.savalli.us/BIO385/Diversity/05.Platyhelminthes.html
http://es.wikipedia.org/wiki/Platyhelminthes
http://www.pbs.org/kcet/shapeoflife/episodes/hunter.html