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

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

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

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: 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

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

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.

Phylum Platyhelminthes: Dugesia

Excretion and osmorregulation: the excretory system consist of canals and protonephridia called flamed cells.

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.

Planaria – cross section

epidermis

rhabditescircular muscle

longitudinal muscle

mesenchyme

intestine

pharynxlumen of pharynx

pharyngeal pouch

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: 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

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.

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: 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

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: Schistosoma1. Ciclo de vida: Observe slides of Schistosoma

mansoni adults, eggs, and cercariae

adults

eggs miracidum cercariae

You need to understand the life cycle

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.

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

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

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.

Uterus

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

Phylum Platyhelminthes: TaeniaTaenia 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