Chapter 34

Section 1Phylum Platyhelminthes

Structure & Function• Bilateral symmetry• Ectoderm, endoderm, mesoderm• No hollow body cavity- acoelomate• Gastrovascular cavity like cnidarians-

single opening• Sensory organs located at the anterior

end of body- cephalization

Structure & Function • Four classes:• Turbellaria- free-living, non-parasitic• Trematoda- parasitic• Monogenea- parasitic• Cestoda- parasitic

Class Turbellaria• Planarians• Arrow-shaped head• Most live in the ocean, some in

freshwater• Glide through the water using mucus

and propelled by cilia

Class Turbellaria• Digestion & Excretion• Scavengers- feed on dead and decaying

matter• Food is ingested by pharynx- runs

through middle of body• Use flame cells to get rid of extra water

since they are constantly taking in water.

Class Turbellaria• Neural control• More complex than cnidarians• Cerebral ganglia- simple brain

(cluster of nerve cells at anterior end)• Eyespots- organism can sense light

with these structures

Class Turbellaria• Reproduction• Hermaphrodites • Sexual reproduction- mate with other

planarians• Asexual reproduction-

regeneration/fission- body splits into two pieces

Classes Trematoda & Monogenea

• Parasitic flukes- leaf-shaped flatworms that parasitize many kinds of animals, including humans• Tremadoes- wide range of hosts-

blood, intestines, lungs, liver, or organs• Monogeneans- ecto-parasites- fish

Classes Trematoda & Monogenea

• Structure• Anterior & ventral sucker• No eye spots• External surface covering- tegument-

helps protect parasite when inside host

Classes Trematoda & Monogenea

• Reproduction & Life Cycle• Hermaphroditic • Primary host- parasite gets

nourishment from• Intermediate host- host from which

the larvae derive their nourishment

Classes Trematoda & Monogenea

• Reproduction & Life Cycle• Schistosomiasis- affects 200 million

people, mostly from Asia, Africa, & South America

Class Cestoda• Tapeworms• Live in intestines of vertebrates• Found in raw or undercooked food

containing eggs or larvae• Causes: weight loss, digestive

problems, lack of energy, etc

Class Cestoda• Structure• Tegument to protect from host

defence• Scolex- knob-shaped organ found at

anterior end of tapeworm- attaches worm to host

Class Cestoda• Structure• Proglottids- long series of body

sections, as it grows it adds proglottids• Can grow up to 33 feet in some cases!• Lack eyespots, sensitive structure, no

mouth, no digestion

Class Cestoda• Reproduction & life Cycle• Hermaphrodites• Cysts- dormant larva with protective

covering

REVIEW!!!• Name the four classes and an example of

each from the Phylum Platyhelminthes.• What kind of nervous system does the

Class Turbellaria have?• Where do tapeworms originate from?

What Class can we find them in?