By: Natalie Williams, Sammy

Keshavarz, Avi Dalal

Platyhelminthes

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).

Sammy Keshavarz

http://i717.photobucket.com/albums/ww179/KingMikey513/ist2_2658206-gummy-worm.jpg

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

• 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

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

• 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

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

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

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

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

• 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

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

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

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

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

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

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

Natalie Williams

Quiz!

4. ANSWER:

b) Absorption through the body wall