14-1 CHAPTER 14 Flat Worms: Phylum Platyhelminthes Flat Worms: Phylum Platyhelminthes

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CHAPTER 14 CHAPTER 14 CHAPTER 14 CHAPTER 14

Flat Worms:Flat Worms:Phylum PlatyhelminthesPhylum Platyhelminthes

Flat Worms:Flat Worms:Phylum PlatyhelminthesPhylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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General FeaturesGeneral Features

Animals that actively seek food, shelter, Animals that actively seek food, shelter,

home sites, and mates require a different set home sites, and mates require a different set of strategies and body organization than of strategies and body organization than radially symmetrical sessile organismsradially symmetrical sessile organisms

Two major evolutionary advances in phylumTwo major evolutionary advances in phylum CephalizationCephalization

Concentrating sense organs in the head regionConcentrating sense organs in the head region Bilateral symmetryBilateral symmetry

Body can be divided along only 1 plane of Body can be divided along only 1 plane of symmetry to yield 2 mirror images of each othersymmetry to yield 2 mirror images of each other

First phylum with Right and Left sidesFirst phylum with Right and Left sides


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General FeaturesGeneral Features

Acoelomates Acoelomates Typical acoelomates have only one internal Typical acoelomates have only one internal

space, the digestive cavityspace, the digestive cavity Without coelom (additional body cavity)Without coelom (additional body cavity)

TriploblasticTriploblastic Endoderm, Ectoderm, and MesodermEndoderm, Ectoderm, and Mesoderm 1st phyla to have 3 germ layers1st phyla to have 3 germ layers

ProtostomesProtostomes blastopore becomes the mouthblastopore becomes the mouth

Incomplete GutIncomplete Gut One opening One opening


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Diagram of an Acoelomate Body Plan


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Phylum PlatyhelminthesPhylum Platyhelminthes

CharacteristicsCharacteristics Commonly called Commonly called flatwormsflatworms Vary from a millimeter to many meters in Vary from a millimeter to many meters in

lengthlength Some free-living; others parasiticSome free-living; others parasitic


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Stained Planaria

Terrestrial flatworm


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Platyhelminthes is divided into Platyhelminthes is divided into three classes:three classes: Turbellaria (Planaria), Trematoda (flukes), and Turbellaria (Planaria), Trematoda (flukes), and Cestoda (tapeworm)Cestoda (tapeworm) All members of All members of Trematoda Trematoda (flukes)(flukes) and and CestodaCestoda

(tapeworms) are (tapeworms) are parasiticparasitic Class TurbellariaClass Turbellaria

Mostly free-living forms Mostly free-living forms Most are bottom dwellers in marine or Most are bottom dwellers in marine or

freshwaterfreshwater Freshwater planarians Freshwater planarians

Found in streams, pools, and hot springsFound in streams, pools, and hot springs Terrestrial flatworms limited to moist placesTerrestrial flatworms limited to moist places



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Form and FunctionForm and Function Epidermis and Muscles Epidermis and Muscles

Most have Most have cellular, ciliated epidermiscellular, ciliated epidermis on a on a basement membranebasement membrane

Most turbellarians have Most turbellarians have dual-gland dual-gland adhesive organsadhesive organs Viscid gland cellsViscid gland cells fasten microvilli of anchor fasten microvilli of anchor

cells to substratecells to substrate Secretions of Secretions of gland cellsgland cells provide a quick provide a quick

chemical detachmentchemical detachment



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Cross Section Of PlanariaTurbellaria


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Releasing and Attaching (Viscid) Glands


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Nutrition and DigestionNutrition and Digestion SomeSome have a mouth, pharynx, and intestine have a mouth, pharynx, and intestine In planariansIn planarians

Pharynx may extend through the ventral mouth Pharynx may extend through the ventral mouth Intestine has three branchesIntestine has three branches

One anterior and two posteriorOne anterior and two posterior Mouth of Mouth of trematodes (parasitic flukes)trematodes (parasitic flukes)

Opens near the anterior endOpens near the anterior end Pharynx is not extensiblePharynx is not extensible Intestine ends blindly, varies in degree of branchingIntestine ends blindly, varies in degree of branching



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Structure of Planarian


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Human Liver Fluke - trematode


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Planaria (Turbellaria)Planaria (Turbellaria) Carnivorous and detect food by Carnivorous and detect food by chemoreceptorschemoreceptors Food trapped in mucous secretions from glandsFood trapped in mucous secretions from glands Wrap themselves around preyWrap themselves around prey Extend the pharynx to suck up bits of foodExtend the pharynx to suck up bits of food



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Trematodes (parasitic flukes)Trematodes (parasitic flukes) Feed on host cells, cellular debris, and body Feed on host cells, cellular debris, and body

fluidsfluids Enzymes from the intestine are secreted for Enzymes from the intestine are secreted for

extracellular digestionextracellular digestion Phagocytic cells in gastrodermis complete Phagocytic cells in gastrodermis complete

digestion at digestion at intracellular levelintracellular level Undigested food egested out the pharynxUndigested food egested out the pharynx

Cestodes (tapeworm)Cestodes (tapeworm) Rely on the host’s digestive tract Rely on the host’s digestive tract Absorb digested nutrientsAbsorb digested nutrients



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Excretion and OsmoregulationExcretion and Osmoregulation Flatworms have Flatworms have protonephridia protonephridia (kidney)(kidney)

Used for Used for osmoregulationosmoregulation Beating flagella drive fluids down collecting ducts Beating flagella drive fluids down collecting ducts

Wall of the duct beyond the Wall of the duct beyond the flame cellflame cell bears folds bears folds

or microvilli to resorb ions and moleculesor microvilli to resorb ions and molecules Majority of metabolic wastes Majority of metabolic wastes

Removed by Removed by diffusiondiffusion through body wall through body wall Collecting ducts join and empty at Collecting ducts join and empty at nephridioporesnephridiopores



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Nervous SystemNervous System Subepidermal nerve plexusSubepidermal nerve plexus resembles resembles

nerve net of cnidariansnerve net of cnidarians One to five pairs of One to five pairs of longitudinal nerve longitudinal nerve

cordscords lie under the muscle layer lie under the muscle layer Freshwater planarians Freshwater planarians

Brain is a Brain is a bilobed cerebral ganglion (mass bilobed cerebral ganglion (mass of nerve cells)of nerve cells) anterior to the ventral nerve anterior to the ventral nerve cordscords



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Sense OrgansSense Organs Ocelli Ocelli (light-sensitive eyespots)(light-sensitive eyespots)

Present in turbellarians, and larval Present in turbellarians, and larval trematodestrematodes

Tactile and chemoreceptive cells Tactile and chemoreceptive cells AbundantAbundant

StatocystsStatocysts (equilibrium) and (equilibrium) and rheoreceptors rheoreceptors (sense direction of water (sense direction of water currents)currents)



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Reproduction and RegenerationReproduction and Regeneration

FissionFission Many turbellarians constrict behind the pharynx and Many turbellarians constrict behind the pharynx and

separate into two animalsseparate into two animals Each half regenerates the missing partsEach half regenerates the missing parts

Provides for Provides for rapid population growthrapid population growth RegenerationRegeneration

If the head and tail are cut offIf the head and tail are cut off Each end grows the missing part; it Each end grows the missing part; it retains polarityretains polarity



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Nearly all are Nearly all are monoecious monoecious (hermaphroditic)(hermaphroditic) but cross-fertilize but cross-fertilize

Male StructuresMale Structures One or more testes are connected to one One or more testes are connected to one

vas deferensvas deferens The vas deferens runs to a seminal vesicleThe vas deferens runs to a seminal vesicle A nipple-like penis or extensible tentacle is A nipple-like penis or extensible tentacle is

the copulatory organthe copulatory organ



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Turbellarians Turbellarians develop male and female develop male and female organs opening at a common pore organs opening at a common pore

After copulation, eggs and yolk cells After copulation, eggs and yolk cells enclosed in small cocoon enclosed in small cocoon Attach by a stalk to plantsAttach by a stalk to plants Embryos emerge and resemble little adultsEmbryos emerge and resemble little adults



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Classification of Phylum PlatyhelminthesClassification of Phylum Platyhelminthes Class Turbellaria - planariaClass Turbellaria - planaria Class Trematoda - flukesClass Trematoda - flukes Class Cestoda - tapewormClass Cestoda - tapeworm



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Class Turbellaria Class Turbellaria Mostly Mostly free-livingfree-living Range from 5 mm to 50 cm longRange from 5 mm to 50 cm long Very small planaria swim by Very small planaria swim by ciliacilia Others move by cilia Others move by cilia

Glide over a Glide over a slime trackslime track secreted by adhesive secreted by adhesive glandsglands

Rhythmical muscular waves pass backward Rhythmical muscular waves pass backward from the headfrom the head



14-25Different Intestinal Pattern of Turbellarians


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Marine tubellarian


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Class TrematodaClass Trematoda All trematodes are parasitic flukesAll trematodes are parasitic flukes Most adults are Most adults are endoparasitendoparasiteses (inside) of vertebrates (inside) of vertebrates They resemble turbellaria but the They resemble turbellaria but the tegument (skin) tegument (skin)

lacks cilia in adultslacks cilia in adults Sense organs are Sense organs are poorly developedpoorly developed Adaptations for parasitism include:Adaptations for parasitism include:

Penetration glandsPenetration glands Hooks and suckers for adhesionHooks and suckers for adhesion Increased reproductive capacityIncreased reproductive capacity



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General Trematoda Life Cycle General Trematoda Life Cycle Egg passes from definitive host and must Egg passes from definitive host and must

reach waterreach water Hatches into a free-swimming ciliated Hatches into a free-swimming ciliated

larva, the larva, the miracidiummiracidium Miracidium penetrates tissues of a snailMiracidium penetrates tissues of a snail

Transforms into a Transforms into a sporocystsporocyst Sporocyst reproduces asexually to form Sporocyst reproduces asexually to form

rediaredia Rediae reproduce asexually and form Rediae reproduce asexually and form

cercariacercaria



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Cercariae emerge from the snail Cercariae emerge from the snail Penetrate a 2Penetrate a 2ndnd intermediate host (fish) intermediate host (fish) Develop into Develop into metacercariaemetacercariae (juvenile flukes) (juvenile flukes)

Metacercaria develop into Metacercaria develop into adultsadults when eaten by when eaten by definitive hostdefinitive host

Some serious parasites of humans and Some serious parasites of humans and domestic animals are trematodesdomestic animals are trematodes Example: sheep live fluke, human liver flukeExample: sheep live fluke, human liver fluke



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Sheep Liver Fluke (Sheep Liver Fluke (Fasciola hepatica)Fasciola hepatica)

Adult fluke lives in bile passageways in the Adult fluke lives in bile passageways in the liver of sheepliver of sheep

Eggs are passed out in feces Eggs are passed out in feces MiracidiaMiracidia hatch and hatch and penetrate snailspenetrate snails to to

become sporocysts become sporocysts After After two generationstwo generations of of rediaerediae

Cercaria Cercaria encyst on vegetation and await being encyst on vegetation and await being eaten by sheepeaten by sheep

When eaten, When eaten, metacercariaemetacercariae develop into develop into young flukesyoung flukes



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Clonorchis sinensisClonorchis sinensis: Human Liver Fluke : Human Liver Fluke Most important human liver flukeMost important human liver fluke Common in China, Japan, and Southeast AsiaCommon in China, Japan, and Southeast Asia Also infects Also infects cats, dogs, and pigscats, dogs, and pigs Adult fluke is 10–20 mm long with an oral and Adult fluke is 10–20 mm long with an oral and

ventral suckerventral sucker



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ClonorchisClonorchis Life Cycle Life Cycle (Liver Fluke) (Liver Fluke) Adults live in Adults live in bile passagewaysbile passageways of humans and other of humans and other

fish-eating mammals (sexual reproduction occurs fish-eating mammals (sexual reproduction occurs here)here)

Eggs containing a Eggs containing a complete miracidiumcomplete miracidium are shed are shed into water with fecesinto water with feces

The eggs hatch only when ingested byThe eggs hatch only when ingested by snails snails of of specific generaspecific genera

Miracidium enters snail tissue and transforms into a Miracidium enters snail tissue and transforms into a sporocyst sporocyst

Sporocyst produces one generation of Sporocyst produces one generation of rediaerediae, which , which begin differentiation (asexual reproduction)begin differentiation (asexual reproduction)



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Human Liver Fluke Life Cycle


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Rediae pass into the snail liverRediae pass into the snail liver Turns into Turns into tadpole-like cercariaetadpole-like cercariae

Cercariae escape into waterCercariae escape into water Make contact with fishMake contact with fish Bore into fish muscles or under Bore into fish muscles or under scalesscales Shed tail and Shed tail and turn into aturn into a metacercariae cyst metacercariae cyst

A mammal eats A mammal eats raw fishraw fish Cyst dissolves and flukes migrate up bile ductCyst dissolves and flukes migrate up bile duct

Heavy infection can Heavy infection can destroy the liverdestroy the liver and and result in deathresult in death

Control of parasitesControl of parasites Destroy snails and thoroughly cook fishDestroy snails and thoroughly cook fish



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Schistosoma: Blood Flukes Schistosoma: Blood Flukes Over 200 million people infested with Over 200 million people infested with

schistosomiasis schistosomiasis Common in Africa, South America, West Indies, Common in Africa, South America, West Indies,

and the Middle and Far Eastand the Middle and Far East Sexes are Sexes are separateseparate 3 species with varied location: 3 species with varied location:

large intestinelarge intestine small intestinesmall intestine urinary bladderurinary bladder



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SchistosomaSchistosoma Life Cycle Life Cycle Eggs discharged in human feces or urineEggs discharged in human feces or urine In water, eggs hatch as ciliated In water, eggs hatch as ciliated miracidiamiracidia Contact with a particular species of Contact with a particular species of snailsnail to to

survive survive In the snail, they transform to In the snail, they transform to sporocysts sporocysts Sporocysts produce Sporocysts produce cercaria cercaria directlydirectly Cercariae Cercariae escape the snailescape the snail and swim until and swim until

they contact they contact bare human skin bare human skin oror other host other host Cercariae Cercariae pierce the skinpierce the skin and shed their tails and shed their tails



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Enter blood vessels and migrate to the Enter blood vessels and migrate to the hepatic portal blood vessels hepatic portal blood vessels (blood vessel (blood vessel from digestive tract to liver)from digestive tract to liver)

Develop in the liver and they migrate to Develop in the liver and they migrate to target sitestarget sites

Eggs released by females are extruded Eggs released by females are extruded through gut or bladder lining and exit with through gut or bladder lining and exit with feces or urinefeces or urine

Eggs that remain behind become Eggs that remain behind become centers of centers of inflammationinflammation



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Blood FlukeLife Cycle


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Cut Liver of individual who dies from hematemesis

(vomiting blood). 180 adult flukes were found in autopsy


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Control: proper disposal of human wastes Control: proper disposal of human wastes Schistosoma dermatitis Schistosoma dermatitis (swimmer’s itch)(swimmer’s itch)

Occurs when cercariae penetrate an unsuitable Occurs when cercariae penetrate an unsuitable host such as a human (our immune system fights host such as a human (our immune system fights them off leading to inflammation -itch)them off leading to inflammation -itch)

Normal host many be a bird or other animalNormal host many be a bird or other animal



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Lung Fluke - from uncooked crab meat


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Class Cestoda Class Cestoda Tapeworms have long flat bodies with Tapeworms have long flat bodies with scolexscolex

Holdfast structure with suckers and hooksHoldfast structure with suckers and hooks

Scolex is followed by a linear series of Scolex is followed by a linear series of reproductive units or reproductive units or proglottids proglottids

Lack a digestive systemLack a digestive system Lack sensory organs except for modified Lack sensory organs except for modified

ciliacilia



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Tapeworm: Scolex is site ofattachment.


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Tegument of aTapeworm:

Many microthricheshelp increase surfacearea for absorption.


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Tegument is has no ciliaTegument is has no cilia Entire surface of cestodes is covered with Entire surface of cestodes is covered with

projections projections (microtriches)(microtriches) similar to similar to microvilli seen in the vertebrate small microvilli seen in the vertebrate small intestineintestine Microtriches increase the surface area for food Microtriches increase the surface area for food

absorptionabsorption



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Nearly all cestodes require two hostsNearly all cestodes require two hosts Adult is parasitic in the Adult is parasitic in the digestive tract of the digestive tract of the

vertebratevertebrate Over 1000 species of tapeworms known, Over 1000 species of tapeworms known,

infecting almost all vertebratesinfecting almost all vertebrates Most tapeworms Most tapeworms do little harm to hostdo little harm to host



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Taenia saginataTaenia saginata: Beef Tapeworm: Beef Tapeworm Lives as an adult in the digestive canals of humansLives as an adult in the digestive canals of humans Juvenile form found in intermuscular tissue of cattleJuvenile form found in intermuscular tissue of cattle Mature adults can reach over 10 meters in length Mature adults can reach over 10 meters in length

with over 2000 proglottids (segments conaining with over 2000 proglottids (segments conaining reproductive organs)reproductive organs)

Scolex has four suckers but no hooksScolex has four suckers but no hooks Gravid proglottidsGravid proglottids (with shelled, infective larvae) (with shelled, infective larvae)

pass in feces, singlepass in feces, single ProglottidsProglottids rupture as they dry rupture as they dry

Embryos are Embryos are viable for five monthsviable for five months and are picked and are picked up by grazingup by grazing



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Beef Tapeworm Life Cycle - ContinuedBeef Tapeworm Life Cycle - Continued Cattle swallow shelled larvae that hatch as Cattle swallow shelled larvae that hatch as

oncospheresoncospheres Oncospheres use hooks to burrow through Oncospheres use hooks to burrow through

the intestinal wall into the intestinal wall into blood or lymph blood or lymph vesselsvessels

When they reach voluntary muscle, they When they reach voluntary muscle, they encyst to become “bladder worms” (cyst that encyst to become “bladder worms” (cyst that resembles a bladder) resembles a bladder)

When the infected meat is eaten, the cyst When the infected meat is eaten, the cyst wall dissolves and the scolex evaginates to wall dissolves and the scolex evaginates to attach to intestinal wallattach to intestinal wall



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New proglottids develop in New proglottids develop in 2–3 weeks 2–3 weeks Infected individuals expel numerous Infected individuals expel numerous

proglottids dailyproglottids daily Infection can be avoided by eating only Infection can be avoided by eating only

thoroughly cooked beefthoroughly cooked beef



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Life Cycle of Beef Tapeworm: From human feces, to grass, to cattle, to meat, to human.


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Dog Tapeworm: Shows 3 Proglottids (Reproductive segments)


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Other types of Tapeworm:Other types of Tapeworm: Taenia soliumTaenia solium: Pork Tapeworm: Pork Tapeworm Diphyllobothrium latumDiphyllobothrium latum: Fish Tapeworm: Fish Tapeworm Echinococcus granulosusEchinococcus granulosus: : Unilocular HydatidUnilocular Hydatid



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Dog Tapeworm: humans acquire disease by unsanitary habits associated with dogs. When eggs are ingested, larvae encyst in the liver, lungs, or other organs.

Cyst enlarges up to the size of a basketball.

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14-1 CHAPTER 14 Flat Worms: Phylum Platyhelminthes Flat Worms: Phylum Platyhelminthes