by: natalie williams, sammy keshavarz, avi dalal platyhelminthes
TRANSCRIPT
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By: Natalie Williams, Sammy
Keshavarz, Avi Dalal
Platyhelminthes
http://www.ucmp.berkeley.edu/platyhelminthes/dugesia.gif
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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).
Sammy Keshavarz
http://i717.photobucket.com/albums/ww179/KingMikey513/ist2_2658206-gummy-worm.jpg
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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
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Cestoda
• 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.
http://www.dogbreedinfo.com/images14/TapewormImg_1384.jpg
Sammy Keshavarz
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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
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Basic Anatomy
Natalie Williams
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Body Cavity
• 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
http://www.cartage.org.lb/en/themes/sciences/zoology/biologicaldiverstity/AnimalsI/flatworm.gif
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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.
Natalie Williams
http://images.google.com/imgres?imgurl=http://www.cartage.org.lb/en/themes/sciences/zoology/biologicaldiverstity/AnimalsI/cavities_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=jdhbfMuz7HljfGwPvzo-mQ&um=1&itbs=1&tbnid=JItKnlsKooaWmM:&tbnh=85&tbnw=130&prev=/images%3Fq%3DPlatyhelminthes%2Bbody%2Bsymmetry%26um%3D1%26hl%3Den%26sa%3DN%26rls%3Dcom.microsoft:en-us:IE-Address%26rlz%3D1I7ADBF_en%26tbs%3Disch:1&ei=-5CYS76FCIrusAPm9s3CAQ
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Nervous System
• Have a cephalized nervous system
• The head ganglion are usually attached to nerve cords connected by transverse branches across the body
Natalie Williams
http://cas.bellarmine.edu/tietjen/Laboratories/platyh5.gif
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Circulatory System
• Platyhelminthes lack a circulatory or respiration system
• Instead, they have absorption through the body wall
Natalie Williams
http://www.historyforkids.org/scienceforkids/biology/animals/flatworms/pictures/flatworm.jpg
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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
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Locomotion/Musculature
• 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. http://www.kingsnake.com/westindian/platyhelminthes2.JPG
Sammy Keshavarz
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Sensory Structures
• 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
http://www.southtexascollege.edu/nilsson/4_GB_Lecture_figs_f/4_GB_23_AnimaliaInvert_Fig_f/Platyhelminthes_Planaria_2.GIF
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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.
Avi Dalal
http://image.tutorvista.com/content/reproduction/planaria-regeneration.jpeg
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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
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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
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Quiz!
1. All of the following classes of Platyhelminthes are parasitic EXCEPT:
a)Tapeworms
b)Monogeneans
c)Planarians
d)Trematodes
Sammy Keshavarz
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Quiz!
1. ANSWER:
c) Planarians
Sammy Keshavarz
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Avi Dalal
Quiz!
2. What are the main sources of sensory input in Platyhelminthes?
a) Gastrovascular cavity
b) Ventral Nerve Cords
c) Ganglia
d) Eyespots
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Avi Dalal
Quiz!
2. ANSWER:
c) Ganglia
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Avi Dalal
Quiz!
3. By which method do Planarians reproduce asexually?
a) Mitosis
b) Meiosis
c) Regeneration
d) Conjugation
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Avi Dalal
Quiz!
3. ANSWER:
c) Regeneration
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Natalie Williams
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
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Natalie Williams
Quiz!
4. ANSWER:
b) Absorption through the body wall