Platyhelminthes
By: Natalie Williams, Sammy
Keshavarz, Avi Dalal
http://www.ucmp.berkeley.edu/platyhelminthes/dugesia.gif
Introduction to Platyhelminthes
• Bilateral Symmetry
• Commonly called
Flatworms because their
bodies are thin between
the dorsal (top side) and
ventral (bottom side)
surfaces
• Include free living and
parasitic species
• Four classes: Turbellaria
(mostly free-living
flatworms), Monogenea
(monogeneans),
Trematoda( trematodes,
or flukes), and Cestoda
(tapeworms).
http://i717.photobucket.com/albums/ww179/KingMikey513/ist2_2658206-gummy-worm.jpg
Sammy Keshavarz
Turbellarians
• Commonly called planarians
• Inhabit unpolluted ponds and streams
• Prey on smaller animals or feed on dead
animals
http://evolution.berkeley.edu/evolibrary/images/evo/planaria.jpg
Sammy Keshavarz
Cestoda
http://www.dogbreedinfo.com/images14/TapewormImg_1384.jpg
• Commonly called
tapeworms
• Parasitic
• The adults live mostly
inside vertebrates,
including humans
• Large tapeworms can
block the intestines and
rob enough nutrients from
the human host to cause
nutritional deficiencies.
Sammy Keshavarz
Monogeneans and Trematodes
• Live as parasites in or
on other animals
• Many have suckers
for attaching to
internal organs or to
other outer surfaces
of the host
• Blood Flukes
(Trematode) have
infected 200 million
people worldwide.
http://www.bergen.edu/faculty/rdill/Environmental_Bio/
EB_lab_Images/schistosoma.jpg
Sammy Keshavarz
Basic Anatomy
Natalie Williams
Body Cavity
http://www.cartage.org.lb/en/themes/sciences/zoology/biologicaldiverstity/AnimalsI/flatworm.gif
• Platyhelminthes have
no body cavity other
than the gut
• They lack an anus so
the same pharyngeal
opening takes in food
and expels waste
• Some tissues and
organs exist but are
not located in the
body cavity.
Natalie Williams
Body Symmetry
• They are unsegmented, bilaterally symmetrical
worms
• Bilateral Symmetry- Only one imaginary cut
divides the animal into mirror-image halves.
• They are triploblastic which means they are
composed of three fundamental cell layers.
http://images.google.com/imgres?imgurl=http://www.cartage.org.lb/en/themes/sciences/zoology/biologicaldiverstity/AnimalsI/c
avities_3.gif&imgrefurl=http://www.cartage.org.lb/en/themes/sciences/zoology/biologicaldiverstity/AnimalsI/AnimalsI.htm&usg
=__tI4qCeEFUImUY9LbxSLS3OpIXNE=&h=325&w=496&sz=31&hl=en&start=14&sig2=jdhbfMuz7HljfGwPvzomQ&um=1&itbs=1&tbnid=JItKnlsKooaWmM:&tbnh=85&tbnw=130&prev=/images%3Fq%3DPlatyhelminthes%2Bbody%2Bsy
mmetry%26um%3D1%26hl%3Den%26sa%3DN%26rls%3Dcom.microsoft:en-us:IEAddress%26rlz%3D1I7ADBF_en%26tbs%3Disch:1&ei=-5CYS76FCIrusAPm9s3CAQ
Natalie Williams
Nervous System
• Have a cephalized
nervous system
• The head
ganglion are
usually attached to
nerve cords
connected by
transverse
branches across
the body
http://cas.bellarmine.edu/tietjen/Laboratories/platyh5.gif
Natalie Williams
Circulatory System
http://www.historyforkids.org/scienceforkids/biology/animals/flatworms/pictures/flatworm.jpg
• Platyhelminthes
lack a circulatory
or respiration
system
• Instead, they
have absorption
through the body
wall
Natalie Williams
Digestive and Excretory System
•
•
•
•
•
A flatworm has a combination
digestive/excretory system. It takes
food in and gets rid of wastes through
the same opening called the pharynx.
Digestive Juices are spilled onto prey,
and the pharynx sucks small pieces of
food into the gastrovascular cavity,
where digestion continues.
Digestion is completed within the cells
lining the gastrovascular cavity,
which has three branches, each with
fine sub branches that provide an
extensive surface area.
Gastrovascular Cavity- A sac with a
central digestive compartment.
The fine branches of gastrovascular
cavity distribute food throughout the
animal.
Sammy Keshavarz
Locomotion/Musculature
http://www.kingsnake.com/westindian/platyhelminthes2.JPG
• A flatworm has no
skeleton.
• Contains three cell layers
called the endoderm, the
mesoderm and the
ectoderm.
• They move by using cilia
(tiny bristles on the
ventral surface) to glide
along a film of mucus
they secrete.
Sammy Keshavarz
Sensory Structures
http://www.southtexascollege.edu/nilsson/4_GB_Lecture_figs_f/4_GB_23_AnimaliaInv
ert_Fig_f/Platyhelminthes_Planaria_2.GIF
• A planarian’s head is
equipped with a pair of light
sensitive eyespots and lateral
flaps that function mainly to
detect specific chemicals.
• The planarian’s nervous
system can adapt and modify
its responses depending on
stimuli.
• Ganglia, located at the
anterior end of the worm, near
the main sources of sensory
input, are a pair of dense
clusters of nerve cells.
• Ventral nerve cords branch
out through the rest of the
body from the ganglia.
Avi Dalal
Reproduction (Methods/Types)
• Planarians can
reproduce asexually
through
regeneration.
• Sexual reproduction
is still possible.
• Since planarians are
hermaphrodites,
sexual reproduction
occurs through the
exchange of sperm.
http://image.tutorvista.com/content/reproduction/planaria-regeneration.jpeg
Avi Dalal
Gas Exchange
• Occurs through diffusion across the body
surface.
• Gas exchange is made easier because
their flat shape places all cells close to the
surrounding water.
• No specialized organs for the function.
• Their relatively simple excretory apparatus
functions mainly to maintain osmotic
balance with their surroundings.
Avi Dalal
Other Unique Features
• Reproductive organs occupy nearly the
entire interior of worms.
• Can manipulate the hosts’ immune system
into tolerating the parasite’s existence.
• Sometimes have alternating sexual and
asexual stages.
• Some parasites can survive in humans for
over 40 years.
Avi Dalal
Quiz!
1. All of the following classes of
Platyhelminthes are parasitic EXCEPT:
a)Tapeworms
b)Monogeneans
c)Planarians
d)Trematodes
Sammy Keshavarz
Quiz!
1. ANSWER:
c) Planarians
Sammy Keshavarz
Quiz!
2. What are the main sources of sensory
input in Platyhelminthes?
a) Gastrovascular cavity
b) Ventral Nerve Cords
c) Ganglia
d) Eyespots
Avi Dalal
Quiz!
2. ANSWER:
c) Ganglia
Avi Dalal
Quiz!
3. By which method do Planarians
reproduce asexually?
a) Mitosis
b) Meiosis
c) Regeneration
d) Conjugation
Avi Dalal
Quiz!
3. ANSWER:
c) Regeneration
Avi Dalal
Quiz!
4. Since Platyhelminthes lack a circulatory
or respiratory system, how do they absorb
those necessary nutrients?
a) They have a circulatory and respiration
system
b) Absorption through the body wall
c) From bacteria that inhabit inside the
organism
d) Absorption from food intake
Natalie Williams
Quiz!
4. ANSWER:
b) Absorption through the body wall
Natalie Williams