Phylum Platyhelminthes

April Adams

Zoology NCHS

Phylum Platyhelminthes• Flat worms• Triploblastic= 3 germ

layers• Acoelomate• Bilateral symmetry• Hermaphroditic• 1 opening for digestion• Simple nervous and

muscular systems• Flame cells• May be free living or

parasitic• CEPHALIZATION

AcoelomateAcoelomate

EctodermMesodermEndoderm

Digestive cavity is the only inner cavity, and is not lined with mesoderm.

Phylum Platyhelminthes: Class Turbellaria

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Acoelomate

Other Body Plans:PseudocoelomateOther Body Plans:Pseudocoelomate

EctodermMesodermEndodermFluid filled cavity between the endoderm and ectoderm- pseudocoelom

Differs from a true coelom because…. • It is not entirely lined with mesoderm tissue• Organs are not suspended or attached to membranes

(mesenteries)

Other Body Plans:Coelomate

Other Body Plans:Coelomate

EctodermMesodermEndoderm

Mesoderm lines cavity between digestive tract and body wall

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Flatworm Body Systems

• No Circulatory or Respiratory systems- simple diffusion through body wall

Systems Present-• Digestive• Nervous • Reproductive• Excretory

Flatworm Body Systems:Digestive

Incomplete-• mouth • pharynx (to swallow

food) • Gastrovascular cavity• intestine(no anus)

Nervous System

Lateral nerve cord

Eye spot= detects light

anterior ganglia

transverse nerve cord

sensory receptors

Cephalization=“Primitive Brain”Cephalization=“Primitive Brain”

Auricle

Cerebral ganglion

Pairednerve cords

Excretory System

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- Gets rid of nitrogenous wastes

- protonephridia- first kidney

Components:- Flame cells- Excretory

ducts/tubes- pores

Reproductive System • Sexual and asexual

reproduction sexual- eggs + sperm asexual- regeneration

• Hermaphrodites- both male (penis and testis)

and female organs(vagina and ovary)

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Checkpoint1. Which phylum do flatworms belong to?2. Flatworms are triploblastic, what does that mean?3. What type of body cavity do they have? Explain.4. Flatworms are the “first” of many things in the animal

kingdom. What traits do flatworms display that were not present in Poriferans, Cnidarians, or Ctenophores?

5. Flatworms have the first excretory system. How does it work?

Kingdom AnimaliaPhylum PlatyhelminthesClasses:

TurbellariaTrematodaCestoda

Class Turbellaria

• Most free-living• Aquatic• Eye spots• Regenerate if cut

in two• Ex. Planaria

Planarians

• Lives in fresh water usually under leaves and rocks

• Usually feeds on dead or slow moving organisms

Planarian Reproduction

Reproduction:• Sexually:

hermaphrodites

• Asexually: can regenerate missing body parts (called fission)

What would happen ????

Detaches its tail end and each half regrows the lost parts

each Planaria gives and receives sperm

Planarians: body structures• Nervous/sensory system: Brain-like structure• Nerve cord: carries impulses down body• Eyespots: sense light and dark• Sensory pits: line sides of head to aid in

movement and sensing surroundings

Planarians: body structuresDigestive/excretory system• Mouth: located in center of

ventral side• Pharynx: tube like structure

which extends from mouth during feeding; acts like a straw sucking up food and carrying it to body

• Food enters mouth and solid wastes exit mouth

• Flame Cells: remove excess water and nitrogenous wastes

eyespot

ganglion

Gastrovascular cavity

Mouth pharynx

Flame cells

ganglion

Nerve cord

(15:00 Sea of Life- Planarian clip)

Class Trematoda• Trema= “hole”• Holdfast devices

– Endoparasites• Complex life cycle- larval

stage in one or more hosts

Primary host-juvenile/larva stage-

Secondary host- adult stage

Ex. Blood and liver flukes

FlukesBlood fluke life cycle:• Eggs are released in water

from wastes of infected host• Hatch in to swimming larvae

in water• Larvae enter a primary host

(like a snail) where they develop & mature to Cercaria stage

• Enter water again and bore into skin of secondary host (man)

• From the blood stream they bore into intestines where they attach and feed on blood

Schistosoma

• Blood flukes• 200 million people• 1 million deaths/year

Life Cycle of a Schistosome Fluke

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Schistosome

• Cercaria have forked tail

Swimmers Itch

Clonorchis sinensis

Oral sucker

Intestine

Uterus

Yolk gland

Testes

Ovary

Seminal recepticle

Clonorchis sinensis

• Chinese liver fluke• 50 million people• Cirrhosis of liver• Diarrhea• Edema• Pain

Fasciola hepatica

• Sheep liver fluke• Sheep, cattle and

man– Weight loss

• Eat contaminated vegetation

Life Cycle of the Sheep Liver Fluke

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Paragonimus westermani

• Lung fluke• Carnivores, pigs,

rodents and man• May be fatal

Class Cestoda: “cess pool”

• Tape worms• All parasitic• Live in intestines of

vertebrates• No digestive system• 40 feet long

Tapeworm structures• Scolex= “head”• hooks and suckers to

aid in attachment to intestine

• Proglottids: individual parts of worm- reproductive– Each one is detachable– Each proglottid may

contain up to 100,000 eggs which fall off when full

– When released, they exit with the host’s wastes

gonad

Tapeworm life cycle• Cows consume contaminated

vegetation, Eggs hatch in intestines of intermediate host (pig or cow)

• Young worms burrow out of intestine into cow’s muscle tissue forming cysts

• Secondary host (man) eats undercooked/raw meat containing worm larvae cysts

• Larvae hatch and mature in intestines, soak up digested food of host

• Proglottids mature, eggs released with feces

• Eggs attach to plant to form cysts

Scolex

Proglottid

Uterus

Testes

Ovary

Yolk gland

Vas deferens

Seminal receptacle

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Pork Tapeworm (Taenia solium)

Taenia saginata

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Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Life Cycle of the Broad Fish Tapeworm

Diphyllobothrium latum

Dipylidium caninum

Echinococcus granulosus

• Parasite of dogs– Host

• Juveniles in sheep, man and other mammals– Intermediate host

• Hydatid cyst

Hydatid Cyst

• Cysticercus – Juvenile stage

• Adult stage in dog

Ecinococcus granulosus

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Checkpoint

1. What are the three classes of flatworms?

2. Which class contains free living species?

3. How do planarians consume food?

4. How are flukes different from Planarians?

5. How are tapeworms different from Trematodes?