18-1 CHAPTER 18 The Ecdysozoas Phylum Nematoda The Ecdysozoas Phylum Nematoda

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CHAPTER 18CHAPTER 18CHAPTER 18CHAPTER 18

The EcdysozoasThe EcdysozoasPhylum NematodaPhylum NematodaThe EcdysozoasThe Ecdysozoas

Phylum NematodaPhylum Nematoda

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Nematode:Trichinella


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DiversityDiversity

Many protostomes possess a Many protostomes possess a cuticlecuticle Non-living outer layer secreted by epidermisNon-living outer layer secreted by epidermis

Cuticle restricts growth and must be molted Cuticle restricts growth and must be molted via via ecdysis (shedding)ecdysis (shedding)

Members of Ecdysozoa molt cuticle as they Members of Ecdysozoa molt cuticle as they growgrow

Regulation of molting achieved by the Regulation of molting achieved by the hormone hormone ecdysoneecdysone

NematodesNematodes are known as Small Ecdysozoans are known as Small Ecdysozoans


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Nematoda (Nematoda (RoundwormsRoundworms) are ) are PseudocoelomatePseudocoelomate Flatworms = acoelomatesFlatworms = acoelomates Complete Guts - mouth and anusComplete Guts - mouth and anus

DiversityDiversity About 25,000 species are described About 25,000 species are described

As many as half a million may existAs many as half a million may exist Found in Found in virtually all habitats in all biomesvirtually all habitats in all biomes

Topsoil may contain Topsoil may contain billions per acrebillions per acre Nematode parasites exist in nearly all Nematode parasites exist in nearly all animal and animal and

plant speciesplant species

DiversityDiversity


Pseudocoelomate - NematodePseudocoelomate - Nematode

EctodermEctodermMesodermMesodermEndodermEndoderm


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Form and FunctionForm and Function Distinguishing CharacteristicsDistinguishing Characteristics

Cylindrical shapeCylindrical shape Nonliving cuticleNonliving cuticle Cuticle shed during juvenile growth stagesCuticle shed during juvenile growth stages

EcdysozoaEcdysozoa Lack motile cilia or flagellaLack motile cilia or flagella Longitudinal muscles in body wallLongitudinal muscles in body wall

Reproduction:Reproduction: Most are Most are dioecious dioecious with males smaller than femaleswith males smaller than females Fertilization is Fertilization is internal internal Eggs are stored in uterus until depositedEggs are stored in uterus until deposited

Phylum Nematoda: RoundwormsPhylum Nematoda: Roundworms


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Female Ascaris (Roundworm)


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Representative Nematode ParasitesRepresentative Nematode Parasites Some are parasites of humansSome are parasites of humans

Most are tropicalMost are tropical Ascaris lumbricoidesAscaris lumbricoides (Roundworm) (Roundworm)

Occurs in Occurs in up to 25% of peopleup to 25% of people in some areas of in some areas of the the southeastern U.S.southeastern U.S.

More than More than 1.27 billion affected worldwide1.27 billion affected worldwide Some species of Ascaris is found in the intestine Some species of Ascaris is found in the intestine

of horse and pigs. of horse and pigs. A female A female AscarisAscaris may lay may lay 200,000 eggs a day200,000 eggs a day, ,

which pass out in host’s feceswhich pass out in host’s feces



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Male and Female Ascaris RoundwormMale is smaller (top), Female is larger


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Viable eggs remain after signs of fecal Viable eggs remain after signs of fecal matter have disappeared matter have disappeared

Survive for long periods in soilSurvive for long periods in soil Host swallows embryonated eggs, juveniles Host swallows embryonated eggs, juveniles

hatch, and burrow through intestinal wallhatch, and burrow through intestinal wall They feed on intestinal contents and They feed on intestinal contents and may may

block or perforate the intestinesblock or perforate the intestines Infection rates tend to be Infection rates tend to be higher in children higher in children

and malesand males



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Life Cycle of Ascaris Roundworm


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HookwormsHookworms Anterior end of these small (9–11 mm) worms has Anterior end of these small (9–11 mm) worms has

a a hook-like curvehook-like curve Necator americanus,Necator americanus, most common hookworm.most common hookworm. Sexes are Sexes are separateseparate Large plates in mouth cut into intestinal wall and Large plates in mouth cut into intestinal wall and

suck host’s bloodsuck host’s blood Pump through more blood than they digestPump through more blood than they digest

Heavy infections cause anemiaHeavy infections cause anemia Eggs pass out in feces and Eggs pass out in feces and juveniles hatch in soiljuveniles hatch in soil If human skin comes in contact with soil, infective If human skin comes in contact with soil, infective

juveniles burrow through skin to bloodjuveniles burrow through skin to blood Travel in blood to the lungs, are coughed up to be Travel in blood to the lungs, are coughed up to be

swallowed, and mature in the intestineswallowed, and mature in the intestine



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Hookworm: A. Mouth showing cutting plates

B. Hookworm attached to dog intestine, cutting plates pinch of intestine wallHookworm secretes an anticoagulant to prevent blood from clotting


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Life cycle of Hookworm


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Trichina WormTrichina Worm Trichinella spiralisTrichinella spiralis causes a potentially lethal causes a potentially lethal

trichinosistrichinosis Adult worms burrow into intestinal wall and Adult worms burrow into intestinal wall and

females directly produce juvenile wormsfemales directly produce juvenile worms Juveniles penetrate blood vessels and circulate Juveniles penetrate blood vessels and circulate

throughout the body to all tissues and spacesthroughout the body to all tissues and spaces Penetrate skeletal muscle cellsPenetrate skeletal muscle cells

Cells lose striations and becomes a nurse cells Cells lose striations and becomes a nurse cells (continues to nourish) to the parasite(continues to nourish) to the parasite

When poorly cooked meat containing encysted When poorly cooked meat containing encysted juveniles is eaten, worms are liberated and juveniles is eaten, worms are liberated and mature in the intestinemature in the intestine

Heavy infection in mammals causes deathHeavy infection in mammals causes death



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Muscle infected withTrichina worm


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Pinworms Pinworms Most Most common worm parasite in the U.S.common worm parasite in the U.S. but causes little but causes little

diseasedisease Adults live in large intestineAdults live in large intestine Females, about 12 mm long, migrate to Females, about 12 mm long, migrate to anal regionanal region at night at night

and lay eggs, causing itchingand lay eggs, causing itching Scratching the anal region Scratching the anal region contaminates hands and contaminates hands and

bedclothesbedclothes Eggs develop rapidly and become infective Eggs develop rapidly and become infective within six hours within six hours

at body temperatureat body temperature When swallowed, hatch in duodenum and mature in large When swallowed, hatch in duodenum and mature in large

intestineintestine Also, pinworms can enter urethra and cause infections in the Also, pinworms can enter urethra and cause infections in the

bladder.bladder. Not to be confused with Candiru - an amazon fish that swims up Not to be confused with Candiru - an amazon fish that swims up

urethraurethra



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A.Female pinworm from intestineB.Group of Pinworm eggs released from anus


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Filarial Worms Filarial Worms Eight species of filarial nematodes infect humansEight species of filarial nematodes infect humans

Some cause serious diseasesSome cause serious diseases Wucheria bancrofti Wucheria bancrofti live in lymphatic systemlive in lymphatic system

Cause inflammation and blockage of the Cause inflammation and blockage of the lymphatics vesselslymphatics vessels

Females release live young, tiny microfilariae, Females release live young, tiny microfilariae, into blood and lymphinto blood and lymph

Mosquitoes ingest microfilariae when they feed Mosquitoes ingest microfilariae when they feed and pass to new host when they feed againand pass to new host when they feed again

ElephantitisElephantitis is caused by repeated exposure is caused by repeated exposure Swelling and growth of connective tissue causes Swelling and growth of connective tissue causes

enormous swelling of body partsenormous swelling of body parts



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Life Cycle of Filarial WormWuchereria bancrofti




African Guinea Worm - Leads to burning/fire pain in leg, fever, vomiting, nausea



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18-1 CHAPTER 18 The Ecdysozoas Phylum Nematoda The Ecdysozoas Phylum Nematoda