PhylumPlatyhelminthes

General Characterisitics• Bilateral symmetry• Acoelomate• Triploblastic• Dorsoventrally Flattened• Un-segmented bodies• Cephalization (has a head)

Characteristics Cont.• 20,000 species• Actual organ systems present

–Nervous, Digestive, Excretory

Taxonomy

• 3 Classes–Class Turbellaria–Class Trematoda–Class Cestoidea

Class Turbellaria

Planarians Free-living bottom-dwellers in

aquatic environmentsfew terrestrial species in the

tropics 3,000+ species Vary widely in color, size, and shape

Terrestrial ones can be up to 60cm

Body Description

3 LayersEctodermMesodermEndoderm

Acoelomate- have a solid mass of mesoderm cells between the ecto- and endo- derms

Acoelomate Design

Locomotion As bottom dwellers the flat

worms glide over the substrate (ground)Use cilia and muscular

contractionsLay down a sheet of mucous

as they travel (like slugs)

Body Systems

Digestive- can be simple or complexPharynx: muscular ingestion organSome digestion takes place outside

the bodyEnzymes secreted on food

particles; helps to break them down so the pharynx can swallow them easier.

Digestive System

Body System Con’t Respiratory- have none

gases are exchanged over the epidermis

CirculatoryProtonephredia: fine networks of

tubes that run the length of the body and collect waste

Flame cells: bulb-like structures that force waste out of the body through openings called nephridiopores.

Excretory System

• Nervous: detecting and responding to environment–Simple: nerve net w/ Statocysts-

sense gravity–Complex: nerve net and two main

nerve cords with ladder like connections between•Auricles: chemoreception•Ocelli: eyespots; detect light

Nervous System

• Reproductive: –Most hermaphrodites–Exhibit both sexual and asexual

• Asexual- transverse fission• Sexual- mutual sperm transfer

Planarian Body Systems

Class Trematoda

• Parasitic flatworms (called flukes)• 1mm to 6cm in size• Most infect internal organs – can

be blood or virtually any other organ

Primary host = the

host in which a

parasite reproduces

sexually

Intermediate host =

the host in which

asexual reproduction

occurs

Fish Flukes

• 30 million people infected in Asia• Caused by eating raw or

improperly cooked fish• Resides in liver bile ducts

• Causes fever, weight loss, joint aches, inflammation, hives, weakness, diarrhea, and an enlarged liver.

Chinese Liver Fluke

More Flukes

• Liver Flukes–Live in the liver bile ducts of

sheep and humans–Host infected by eating aquatic

vegetation (watercress)

• Schistosomes: blood flukes–Millions infected worldwide–Causes rash, fever, chills,

inflammation, liver and spleen enlargement.

Schistosoma mansoni - multiple host:

Primary host = human

Intermediate host = snail

Causes Schistosomiasis -in humans; decays

lungs liver, spleen, or intestines, occurs in

tropical areas with poor sanitation/sewage.

Blood Fluke

Class Cestoidea

• Tapeworms• 3,500 species• All are endo-parasites of

vertebrates

Lack a mouth and digestive tract Body consists of 3 main parts

scolex: hold fast structureStrobila: the neck regionProglottids: reproductive sacs

that make up 90 percent of the body

Each mature proglottid is a

hermaphrodite

Testes produce sperm, fertilize the

eggs to produce a zygote

Zygotes are

passed out

through the

feces.

Sometimes, a dormant, protective cyst is

formed in the intermediate host muscles

****This is why you should never eat

incompletely cooked meat.

Tapeworm Life cycle

Tapeworm Life Cycle