FLATWORMSKingdom Animalia

Phylum PlatyhelminthesEx. Planaria, flukes and tapeworms

Class CestodaClass Turbellaria

Class Trematoda

Characteristics of Platyhelminthes • Body symmetery: bilateral• Body organization: triploblastic (3 layers)

– Ectoderm– Mesoderm (first!!)– Endoderm

• Body Cavity: acoelomate

Characteristics continued

• Digestive system: mouth & gastrovascular cavity

• Reproduction: – Sexual:

hermaphroditic – cross fertilization occurs between 2 worms

– Asexual: fragmentation

Characteristics continued:• Circulation: diffusion• Nervous system:

– Cephalization (first) & nerves

– Eyespots, auricles, sensitive to light & chemicals

• Respiration: diffusion through skin

• Excretion: tubes open to outside, flame cells (rid of excess H2O)& mouth

• Habitat: host (intestine) & freshwater

• Ecological roles:– Parasitic– Food source– Eat dead animals

• saprophytes

Additional information:

Free living

ex) Planaria – freshwater Stores food as fat Brain coordinates

movement & capable of learning its way through a maze

Able to respond to light & chemicals

Additional information:

ParasiticEx) flukes and tapeworms• Lives in digestive tract

& absorbs digested food from host so, NO digestive tract!

• This leaves more room for reproduction – capable of producing 1,000s of eggs.

Platyhelminthes vs Cnidarians• Tissues organized into

organs– Reproductive system

(organized organs)

• Three embryonic tissue layers– Mesoderm

• Bilateral Symmetry• Cephalization and

nerve cords

• No true organs

• Two Tissue layers

• Radial Symmetry• Nerve Net

**DO NOT COPY

Class Cestoda

• AKA tapeworms• Tapeworms are parasites that live in the

digestive system of vertebrate animals

More on Tapeworms…• Specialized for living within a host

– Lost most body systems• No digestive, nervous, excretory, muscle systems• Absorb food by diffusion through skin

– Has specialized reproduction

Tapeworm Reproduction• Specialized body sections called proglottids

– Hermaphroditic• Contain both ovaries and testes• Can fertilize their own eggs

– Zygotes are passed out of host’s body with feces– Larvae hatch in water and in grass

• Eaten by herbivore (intermediate host) – larvae then burrows through wall of intestine and into blood stream

• Intermediate host contains tapeworm cysts (bladder worm)– when ingested by final host (e.g. human) cyst hatches out as scolex which then grows proglottids

**DO NOT COPY**

Tapeworm cont’d• Two body regions

– Scolex – “head”• No cephalization• Hooks and suckers used to attach to inside wall of

intestine– Proglottids

• Body segments for reproduction

Tapeworm life cycle

Fun Facts About Tapeworms• Some tapeworms grow quite long. One species that

parasitizes horses has been known to attain a length of 75 feet.

• Ingesting tape worms for reducing weight is a diet routine: A rather surprising fact about tape worms is that ingesting them as a weight-loss technique is happening even in these modern times. The person undergoing this method has the direct risk of an infection. It also causes a dramatic reduction in the body’s ability to absorb nutrients; and a counter-effect, where the person eats more to balance the metabolic stress once the diet regime is over.

**DO NOT COPY**

Class Trematoda

Ex: Chinese liver fluke

Fluke (liver, lung, heart, intestine)• Parasitic

– Pharynx swallows host’s tissue and body fluids (including blood)

– Common intermediate host: raw fish• No need for circulation or respiratory

system– Live in tissues supplied by host’s blood– Absorb through gastrovascular cavity

• Flame cells• Nerve cords and anterior ganglia

– Do not have as specialized nerve cells like Planaria

• Hermaphrodites– Complex life cycle with numerous larval

stages that infect a number of hosts.

Liver Fluke Life Cycle

Blood Flukes

liver fluke

Class Turbellaria

Planaria• Excretion

– Two networks of tubes– Attached to tubes are flame cells

• Modified to work like a kidney• Have cilia that cause excess body

fluid to move along excretory tubes and eventually out of planaria body

• Muscles– Three layers of muscles below ectoderm– Constrict – shorten, and flatten worm.

Flame Cell1. Cell Nucleus2. Bundle of Cilia (flame)3. Parenchyma Tissue 4. Collecting Duct

1. Pharynx

2. Auricle

3. Eye spot

4. Pharynx

5. Gastrovascular cavity

Marine Flatworms

Flatworms are hermaphrodites

When flatworms encounter each other, they engage in a 60 minute ‘dance’ during which they repeatedly strike at each other, both trying to inject their sperm under the skin of the other worm.

The ‘winner’ becomes the male for that encounter, and the ‘loser’ must become the female & care for the fertilized eggs!

https://www.youtube.com/watch?v=wn3xluIRh1Y