phylum platyhelminthes. general characterisitics bilateral symmetry acoelomate triploblastic...
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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