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Phylum Platyhelminthes
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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
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Phylum Platyhelminthes: flatworms
These are acoelomate metazoans
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)
Porif
era
Parazoa
Deu
tero
stom
ia
Ecdy
sozo
a
Anne
lida
Mol
lusc
a
Loph
opho
rata
Rotif
era
Plat
yhel
min
thes
Lophotrochozoa
Eumetazoa
BilateriaRadiata
Protostomia
Cnid
aria
and
Cte
noph
ora
Lophotrochozoa
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Phylum Platyhelminthes: Classification
Turbellaria: • Ciliated epidermis• Paraphyletic group• Mostly free-living
Classes:
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
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
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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
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Phylum Platyhelminthes: Dugesia1. Take a slide from your box with a planaria: identify
the eyespot, aurículas, intestino, faringe, y boca.
What is the function of the eyespot and the auricles? ____________ Check your book for answers!
bocaintestino
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Phylum Platyhelminthes: DugesiaAs 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
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Phylum Platyhelminthes: DugesiaReproduction: 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.
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 reproductionPlanarians 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.
sexual reproductionPlanarians 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.
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Phylum Platyhelminthes: Dugesia
Excretion and osmorregulation: the excretory system consist of canals and protonephridia called flamed cells.
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Phylum Platyhelminthes: Dugesia2. Take a slide from your box with a planaria cross
section cuts: identify intestino, diverticulos intestinal, lumen de la faringe, musculos dorsoventrales.
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Planaria – cross section
epidermis
rhabditescircular muscle
longitudinal muscle
mesenchyme
intestine
pharynxlumen of pharynx
pharyngeal pouch
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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?
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Phylum Platyhelminthes: Dugesia4. 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
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Phylum Platyhelminthes: Dugesia5. 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.
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.
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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
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Phylum Platyhelminthes: Clonorchis1. 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
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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
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Phylum Platyhelminthes: Schistosoma1. Ciclo de vida: Observe slides of Schistosoma
mansoni adults, eggs, and cercariae
adults
eggs miracidum cercariae
You need to understand the life cycle
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Phylum Platyhelminthes: Your TasksPhylum: 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.
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Phylum Platyhelminthes: Taenia1. 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
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Phylum Platyhelminthes: Taenia1. 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= suckersB=hooks scolex
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Phylum Platyhelminthes: Taenia2. 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.
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Uterus
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Phylum Platyhelminthes: Taenia2. 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
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Phylum Platyhelminthes: TaeniaTaenia life cycle
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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