Biology 320 Invertebrate Zoology Fall 2005 Chapter 10 – Phylum Platyhelminthes.

Biology 320Biology 320Invertebrate ZoologyInvertebrate Zoology

Fall 2005Fall 2005

Chapter 10 – Phylum Chapter 10 – Phylum PlatyhelminthesPlatyhelminthes

Phylum PlatyhelminthesPhylum Platyhelminthes

20,000 species of soft, 20,000 species of soft, dorsoventrally compressed dorsoventrally compressed wormsworms

Mainly marine or freshwaterMainly marine or freshwater

Three major groupsThree major groups Class Turbellaria – free-living Class Turbellaria – free-living

flatwormsflatworms Class Trematoda – parasitic Class Trematoda – parasitic

flukesflukes Class Cestoda – parasitic Class Cestoda – parasitic

tapewormstapeworms

Most are acoelomate and also Most are acoelomate and also lack a hemal systemlack a hemal system

Small size is an adaptation to Small size is an adaptation to living in tight spaces, such as living in tight spaces, such as under rocks, in body cavities, under rocks, in body cavities, etc.etc.

Class TurbellariaClass Turbellaria

Two types, grouped Two types, grouped according to sizeaccording to size MicroturbellariaMicroturbellaria MacroturbellariaMacroturbellaria

MicroturbellariaMicroturbellaria The majority of The majority of

turbellarians at 4500 turbellarians at 4500 spp.spp.

0.5mm – a few mm0.5mm – a few mm

MacroturbellariaMacroturbellaria Normally several cmNormally several cm Largest lives in a lake in Largest lives in a lake in

Russia and can reach Russia and can reach 60cm in length60cm in length

Body WallBody Wall

Typically have one layer of ciliated epidermisTypically have one layer of ciliated epidermis

Cilia may only be present on ventral surfaceCilia may only be present on ventral surface

Name means “whirlpool,” due to ciliary actionName means “whirlpool,” due to ciliary action

Microvilli also present on epidermisMicrovilli also present on epidermis

Soft; lack a cuticleSoft; lack a cuticle

Often have a fibrous Often have a fibrous endoskeleton endoskeleton containing actin containing actin filamentsfilaments

Epidermis is glandular; Epidermis is glandular; secretes:secretes: MucusMucus AdhesivesAdhesives RhabdoidsRhabdoids

RhabdoidsRhabdoids Membrane-boundMembrane-bound Rod-shapedRod-shaped Released onto Released onto

epidermal surfaceepidermal surface Expand to form mucusExpand to form mucus Rhabdite is the most Rhabdite is the most

common typecommon type

Adhesion Adhesion facilitated byfacilitated by GlandsGlands CiliaCilia Muscular suckersMuscular suckers

Many have Many have structures known structures known as duo-gland as duo-gland organsorgans Consists of two Consists of two

different kinds of gland different kinds of gland cells in one complexcells in one complex

Viscid gland secretes Viscid gland secretes adhesiveadhesive

Releasing gland Releasing gland secretes de-adhesivesecretes de-adhesive

Musculature Musculature and and

LocomotionLocomotion Fairly complex musculatureFairly complex musculature

Typical circular and longitudinalTypical circular and longitudinal DiagonalDiagonal DorsoventralDorsoventral

Capable of many types of Capable of many types of movementmovement Ciliary glidingCiliary gliding CreepingCreeping Swimming using dorsoventral Swimming using dorsoventral

undulations of lateral body undulations of lateral body marginsmargins

TwistingTwisting SomersaultingSomersaulting

Nervous SystemNervous System

VariableVariable

Primitive flatworms Primitive flatworms Ring-like brainRing-like brain One or more nerve cords One or more nerve cords

extending posteriorlyextending posteriorly Nerve netNerve net

DugesiaDugesia, and similar worms , and similar worms Bilateral brainBilateral brain Two ventrolateral Two ventrolateral

longitudinal nerve cordslongitudinal nerve cords Transverse commissures Transverse commissures

that give the nervous that give the nervous system an ladder-like system an ladder-like appearanceappearance

Sensory structuresSensory structures Usually two pigment cup ocelliUsually two pigment cup ocelli

PhotoreceptorsPhotoreceptors Many flatworms are negatively Many flatworms are negatively

phototacticphototactic

Some possess statocystsSome possess statocysts Balance and orientationBalance and orientation

MechanoreceptorsMechanoreceptors Senses pressure, touch, etc.Senses pressure, touch, etc.

NutritionNutrition Most posses a blind gut used Most posses a blind gut used for ingestion and egestionfor ingestion and egestion

Extremely long flatworms Extremely long flatworms have a through-guthave a through-gut

A single layer of gastrodermis A single layer of gastrodermis lines gutlines gut PhagocytesPhagocytes GlandularGlandular Ciliated in more primitive Ciliated in more primitive

turbellariansturbellarians

Gut design varies depending Gut design varies depending on body sizeon body size Microturbellaria have simple, Microturbellaria have simple,

unbranched gutsunbranched guts Macroturbellaria often have Macroturbellaria often have

digestive ceca to increase SA digestive ceca to increase SA for digestion, absorption, etc.for digestion, absorption, etc.

Location of mouth Location of mouth variesvaries Usually located mid-Usually located mid-

ventrally, but anywhere ventrally, but anywhere along the ventral midlinealong the ventral midline

Presence / absence / Presence / absence / type of pharynx variestype of pharynx varies Zero pharynx – no Zero pharynx – no

pharynxpharynx

Simple pharynx – ciliated Simple pharynx – ciliated tubetube

Plicate pharynx – long, Plicate pharynx – long, muscular, protrusible muscular, protrusible tube. Housed in a sheath tube. Housed in a sheath when retractedwhen retracted

Bulbous pharynx – Bulbous pharynx – muscular sucking bulb; muscular sucking bulb; can be everted in somecan be everted in some

Type of prey is related to pharynx structure Type of prey is related to pharynx structure and body sizeand body size Small - bacteria, unicellular algae, and protozoansSmall - bacteria, unicellular algae, and protozoans Large - small inverts such as rotifers, insect Large - small inverts such as rotifers, insect

larvae, crustaceans, and annelidslarvae, crustaceans, and annelids

Most are carnivorous, but some are Most are carnivorous, but some are scavengersscavengers

Many methods of prey captureMany methods of prey capture Wrap around preyWrap around prey Entangle in mucus (sometimes toxic)Entangle in mucus (sometimes toxic) Capture with everted raptorial proboscis (has Capture with everted raptorial proboscis (has

adhesive cups or hooks)adhesive cups or hooks) Pin prey to substrate with adhesive organsPin prey to substrate with adhesive organs Some even stab with penis stylet Some even stab with penis stylet

May ingest whole prey items or pieces of preyMay ingest whole prey items or pieces of prey

Eversible pharynx penetrates prey or carrion, and pumps Eversible pharynx penetrates prey or carrion, and pumps contents into gutcontents into gut

DigestionDigestion Extracellular initially. Pharynx is muscular and often has Extracellular initially. Pharynx is muscular and often has

enzyme releasing pharyngeal glandsenzyme releasing pharyngeal glands Intracellular laterIntracellular later

Can withstand long periods of starvation by reabsorbing Can withstand long periods of starvation by reabsorbing and metabolizing gut tissue, reproductive tissue, and and metabolizing gut tissue, reproductive tissue, and various connective tissuesvarious connective tissues

SymbiosisSymbiosis

Some harbor Some harbor endosymbiotic endosymbiotic photosynthesizersphotosynthesizers

Some are commensals of Some are commensals of molluscs and arthropodsmolluscs and arthropods BdellouraBdelloura lives on gills of lives on gills of

horseshoe crabshorseshoe crabs Shares food collected by hostShares food collected by host

Several are Several are endoparasites of endoparasites of molluscs, crustaceans, molluscs, crustaceans, and echinodermsand echinoderms

Internal TransportInternal Transport

Most lack a coelom and hemal systemMost lack a coelom and hemal system

Vermiform design and flatness provides large Vermiform design and flatness provides large SA:volSA:vol

Gas exchange occurs across body wall and general Gas exchange occurs across body wall and general body surfacesbody surfaces

Nutrient circulation and diffusionNutrient circulation and diffusion Simple gut is not diffusion limitedSimple gut is not diffusion limited Digestive ceca provide enough surface area to meet Digestive ceca provide enough surface area to meet

diffusion requirements in larger wormsdiffusion requirements in larger worms Gastrodermis has cilia for circulation Gastrodermis has cilia for circulation

ExcretionExcretion Nitrogen from protein Nitrogen from protein

metabolism is in the form of metabolism is in the form of ammoniaammonia

Released along with water and Released along with water and other metabolitesother metabolites

Protonephridia are the Protonephridia are the excretory “organs”excretory “organs”

Posses lots of protonephridia, Posses lots of protonephridia, as there is no circulatory as there is no circulatory system to pump blood to a system to pump blood to a centralized kidneycentralized kidney

Essentially a cup with ciliated Essentially a cup with ciliated terminal cellsterminal cells

Cilia draw fluid into cupCilia draw fluid into cup

Cup filters fluid through a Cup filters fluid through a mesh-like structuremesh-like structure

Waste travels through ducts Waste travels through ducts which open to the surface via which open to the surface via porespores

AsexualAsexual Reproduction Reproduction

RegenerationRegeneration Amazing regenerators (1/300Amazing regenerators (1/300thth

of body can grow into an entire of body can grow into an entire worm)worm)

Active area of researchActive area of research Interesting patterns of Interesting patterns of

regeneration, depending on regeneration, depending on where the animal is cutwhere the animal is cut

ClonalClonal Transverse fission – posterior Transverse fission – posterior

end attaches, anterior end pulls end attaches, anterior end pulls and separatesand separates

Paratomy – resembles Paratomy – resembles strobilation in cnidariansstrobilation in cnidarians

Fragmentation – cyst forms Fragmentation – cyst forms around fragment. Regeneration around fragment. Regeneration occurs and cyst hatchesoccurs and cyst hatches

Parthenogenesis – “virgin birth”Parthenogenesis – “virgin birth”

Sexual ReproductionSexual Reproduction

HermaphroditicHermaphroditic

Male organsMale organs Two testes that each lead to a sperm duct… Two testes that each lead to a sperm duct… Then to a seminal vesicle (storage)Then to a seminal vesicle (storage) Penis – copulatory organ that may be armed Penis – copulatory organ that may be armed

with a sharp, hardened styletwith a sharp, hardened stylet

Female organsFemale organs Gonopore for copulationGonopore for copulation Copulatory bursa for short term storage of Copulatory bursa for short term storage of

partners spermpartners sperm Seminal receptacle for long term sperm storageSeminal receptacle for long term sperm storage

CopulationCopulation ReciprocalReciprocal Rarely self fertilizeRarely self fertilize Internal fertilizationInternal fertilization Hypodermic Hypodermic

impregnationimpregnation

EggsEggs Oviposited from Oviposited from

gonopore (singly, gonopore (singly, clutches, strings)clutches, strings)

Relatively few eggsRelatively few eggs Carefully spawned and Carefully spawned and

have protective capsuleshave protective capsules Some FW spp. produce Some FW spp. produce

both summer eggs and both summer eggs and resting (winter) eggsresting (winter) eggs

Usually direct Usually direct developmentdevelopment

Some produce Some produce planktotrophic larvaeplanktotrophic larvae

Diversity of Class TurbellariaDiversity of Class Turbellaria

Order CatenulidaOrder Catenulida Small, long, and slenderSmall, long, and slender Few epidermal ciliaFew epidermal cilia Head has one statocyst Head has one statocyst

and two ciliated pitsand two ciliated pits Mouth opens into Mouth opens into

simple pharynxsimple pharynx Gonads unpairedGonads unpaired Aflagellate spermAflagellate sperm May reproduce via May reproduce via

paratomyparatomy CatenulaCatenula

Order AcoelaOrder Acoela Less than 2mm longLess than 2mm long Many cilia on Many cilia on

epidermisepidermis No pharynxNo pharynx Lack cellular gutLack cellular gut Individual germ cells Individual germ cells

rather than gonadsrather than gonads Biflagellate spermBiflagellate sperm No oviduct, eggs No oviduct, eggs

rupture wallrupture wall No protonephridiaNo protonephridia AmphiscolopsAmphiscolops

Order MacrostomidaOrder Macrostomida

Lots of epidermal ciliaLots of epidermal cilia

RhabditesRhabdites

Duo-glandsDuo-glands

Small paired ocelliSmall paired ocelli

Simple pharynxSimple pharynx

One pair of ventrolateral nerve cords w/ One pair of ventrolateral nerve cords w/ commissurescommissures

Aflagellate spermAflagellate sperm

MacrostomumMacrostomum

Order PolycladidaOrder Polycladida Many epidermal ciliaMany epidermal cilia

Rhabdites and duo-Rhabdites and duo-gland organsgland organs

Biflagellate spermBiflagellate sperm

Plicate pharynxPlicate pharynx

Large, up to 30cmLarge, up to 30cm

Oval, flattenedOval, flattened

Large gut w/ many Large gut w/ many cecaceca

Some produce larvaeSome produce larvae

May be brightly May be brightly colored (aposematic in colored (aposematic in some)some)

StylochusStylochus

Order TricladidaOrder Tricladida

Many epidermal ciliaMany epidermal cilia

Rhabdites and duo-gland Rhabdites and duo-gland organsorgans

Biflagellate spermBiflagellate sperm

Plicate pharynxPlicate pharynx

Yolky eggsYolky eggs

Large gut with three Large gut with three branches and many cecabranches and many ceca

BdellouaBdelloua, , DugesiaDugesia

Order RhabdocoelaOrder Rhabdocoela

Several subordersSeveral suborders

Many epidermal ciliaMany epidermal cilia

Rhabdites and duo-Rhabdites and duo-gland organsgland organs

Biflagellate spermBiflagellate sperm

Protrusible bulbous Protrusible bulbous pharynxpharynx

Some have proboscis Some have proboscis which can be evertedwhich can be everted

Some have ventral Some have ventral adhesive discadhesive disc

MesostomaMesostoma

NeodermataNeodermata

Flukes, tapeworms and Flukes, tapeworms and relatives belong to the relatives belong to the taxon Neodermatataxon Neodermata

Cellular epidermis is later Cellular epidermis is later replaced with syncytium replaced with syncytium called neodermiscalled neodermis Non-ciliatedNon-ciliated

No intracellular spaces due No intracellular spaces due to syncytiumto syncytium One multinucleate cellOne multinucleate cell Nothing unwanted passesNothing unwanted passes

Class TrematodaClass Trematoda

FlukesFlukes

Belong to Subclass Belong to Subclass Digenea, which means Digenea, which means “two generations”“two generations”

Endoparasites of Endoparasites of vertebratesvertebrates

11,000 spp.11,000 spp.

Body Form and FunctionBody Form and Function

FlatFlat

0.2 mm – 6.0 cm long0.2 mm – 6.0 cm long

Various adhesion devicesVarious adhesion devices Oral sucker surrounding Oral sucker surrounding

mouthmouth Ventral suckerVentral sucker

Facultative anaerobes that Facultative anaerobes that mainly rely on glycolysismainly rely on glycolysis

Neodermis helps protect Neodermis helps protect against host’s digestive against host’s digestive enzymesenzymes

Circular, longitudinal, and diagonal Circular, longitudinal, and diagonal musculaturemusculature

Nervous systemNervous system Similar to that of the turbellariansSimilar to that of the turbellarians Pair of anterior cerebral ganglia (brain)Pair of anterior cerebral ganglia (brain) Longitudinal nerve cords (variable)Longitudinal nerve cords (variable) Ocelli in infective larval stages (miracidia and Ocelli in infective larval stages (miracidia and

cercaria)cercaria)

Excretory systemExcretory system ProtonephridiaProtonephridia Two longitudinal collecting ductsTwo longitudinal collecting ducts Posterior bladderPosterior bladder One nephridioporeOne nephridiopore

ReproductionReproduction

Highly organized Highly organized reproductive systemreproductive system

Constant supply of Constant supply of nutrients from host allow nutrients from host allow for large egg productionfor large egg production 10,000 to 100,000 that of 10,000 to 100,000 that of

turbellariansturbellarians

Male systemMale system Two testesTwo testes Two ductsTwo ducts External seminal vesicleExternal seminal vesicle Cirrus sac (internal Cirrus sac (internal

seminal vesicle, prostate, seminal vesicle, prostate, copulatory cirrus)copulatory cirrus)

Genital atrium shared between male and female Genital atrium shared between male and female reproductive systems; contains one gonoporereproductive systems; contains one gonopore

Female systemFemale system One ovary (germarium)One ovary (germarium) Oviduct - where seminal vesicles and vitellaria (yolk Oviduct - where seminal vesicles and vitellaria (yolk

producing structures) are added producing structures) are added Ootype (sac which encapsulates egg and yolk cells in Ootype (sac which encapsulates egg and yolk cells in

protein)protein) UterusUterus To genital atrium; out gonoporeTo genital atrium; out gonopore

Some dioecious, but most are Some dioecious, but most are monoeciousmonoecious

Most cross-fertilize, but some can self-Most cross-fertilize, but some can self-fertilizefertilize

No asexual reproduction in adultsNo asexual reproduction in adults No need, as adults usually have a constant No need, as adults usually have a constant

supply of nutrientssupply of nutrients

Asexual reproduction in some larval Asexual reproduction in some larval stagesstages

Trematode Life CyclesTrematode Life Cycles Two or more hosts / infective larval stagesTwo or more hosts / infective larval stages

11stst intermediate host is usually a gastropod mollusc (snail) intermediate host is usually a gastropod mollusc (snail) 22ndnd intermediate host is usually an arthropod or fish intermediate host is usually an arthropod or fish Definitive host is a vertebrateDefinitive host is a vertebrate

Aquatic cycle (may also occur on land)Aquatic cycle (may also occur on land) Eggs are passed in fecesEggs are passed in feces If land in water, hatch as miracidia (infect snails) If land in water, hatch as miracidia (infect snails) Miracidium sloughs off epidermis and metamorphoses into Miracidium sloughs off epidermis and metamorphoses into

sporocyst, which contains many embryossporocyst, which contains many embryos Sporocyst embryos form redia (feeding larvae with digestive Sporocyst embryos form redia (feeding larvae with digestive

system; also produce embryos)system; also produce embryos) Redia embryos develop into cercaria (possess digestive tract, Redia embryos develop into cercaria (possess digestive tract,

suckers and tail)suckers and tail) Cercaria leave snail, swim, and infect 2Cercaria leave snail, swim, and infect 2ndnd intermediate host intermediate host

(usually arthropod or fish), and encyst as metacercaria(usually arthropod or fish), and encyst as metacercaria Definitive host eats infected muscle tissue, and metacercaria Definitive host eats infected muscle tissue, and metacercaria

develops into adultdevelops into adult Free metacercaria can also be found attached to rocks or Free metacercaria can also be found attached to rocks or

aquatic plantsaquatic plants

Chinese Liver FlukeChinese Liver Fluke

OpisthorchisOpisthorchis (or (or ChlonorchisChlonorchis) ) sinensissinensis

Infects bile ducts of 20 million people in Infects bile ducts of 20 million people in AsiaAsia

Adults are 2.5 cm longAdults are 2.5 cm long

Live up to 8 yearsLive up to 8 years

Produce 4000 eggs / dayProduce 4000 eggs / day

Causes jaundice, gallstones, and Causes jaundice, gallstones, and possibly liver cancer possibly liver cancer

Blood FlukeBlood Fluke

Schistosoma mansoniSchistosoma mansoni

Found in neotropics, and AfricaFound in neotropics, and Africa

Causes schistosomiasisCauses schistosomiasis 300 million people worldwide300 million people worldwide One of three worst parasitic diseasesOne of three worst parasitic diseases

DioeciousDioecious Male and female permanently pairedMale and female permanently paired Smaller female fits in groove on Smaller female fits in groove on

malemale

Live in intestinal veinsLive in intestinal veins Eggs laid in venulesEggs laid in venules Work way into lumen using spikes / Work way into lumen using spikes /

enzymesenzymes

Life cycle is typical of Life cycle is typical of trematodestrematodes

Cercaria penetrate human Cercaria penetrate human skin w/ enzymes and skin w/ enzymes and muscular boringmuscular boring

Enter circulation and Enter circulation and transform into adults on transform into adults on way to intestineway to intestine First pass through lungs First pass through lungs

and liverand liver

Damage to organs and Damage to organs and vessels from various life vessels from various life stages (eggs are the worst)stages (eggs are the worst)

Causes inflammation, Causes inflammation, necrosis, and fibrosisnecrosis, and fibrosis

Class MonogeneaClass Monogenea 1100 spp.1100 spp.

Typically 1 – 5 mm long, but Typically 1 – 5 mm long, but up to 20 mmup to 20 mm

Mainly ectoparasites of Mainly ectoparasites of aquatic vertebrates; therefore aquatic vertebrates; therefore rely on aerobic metabolismrely on aerobic metabolism

Name means “one Name means “one generation,” because they generation,” because they lack clonal reproductionlack clonal reproduction

Also lack intermediate hostsAlso lack intermediate hosts

Have a large attachment Have a large attachment organ organ Known as a haptorKnown as a haptor Located posteriorlyLocated posteriorly Has suckers and hooksHas suckers and hooks

Egg develops into a hooked Egg develops into a hooked miracidiummiracidium

Called oncomiracidiumCalled oncomiracidium Has two ocelliHas two ocelli

AdultAdult Head (sometimes has Head (sometimes has

muscular oral sucker, or muscular oral sucker, or adhesive glands)adhesive glands)

TrunkTrunk HaptorHaptor

Pharynx secretes protease Pharynx secretes protease which degrades host’s which degrades host’s epidermisepidermis

Feed on:Feed on: Cellular debrisCellular debris BloodBlood mucusmucus

Remaining body systems are Remaining body systems are similar to turbellarians and similar to turbellarians and trematodestrematodes

Life CyclesLife Cycles DactylogyrusDactylogyrus

Ectoparasite of fish gillsEctoparasite of fish gills Serious problem in hatcheriesSerious problem in hatcheries Leads to death by blood loss or Leads to death by blood loss or

secondary infectionsecondary infection

PolystomaPolystoma Inhabits bladders of old world frogsInhabits bladders of old world frogs Synchronization of life cycles (host Synchronization of life cycles (host

and parasite eggs released at same and parasite eggs released at same time)time)

Oncomiracidia attach to tadpole’s gillsOncomiracidia attach to tadpole’s gills When tadpole becomes frog, parasite When tadpole becomes frog, parasite

migrates from gill chamber to bladdermigrates from gill chamber to bladder

Class CestodaClass Cestoda The tapewormsThe tapeworms

3400 spp.3400 spp.

All endoparasites of vertebrate gutsAll endoparasites of vertebrate guts

Lack gut entirelyLack gut entirely

Long; can reach 25 mLong; can reach 25 m

Body FormBody Form Ribbon-likeRibbon-like

Three regionsThree regions Scolex – head with hooks and suckers Scolex – head with hooks and suckers

for attachmentfor attachment Neck – narrow growth zone containing Neck – narrow growth zone containing

stem cellsstem cells Strobila – segmented trunk consisting Strobila – segmented trunk consisting

of proglottids (segments)of proglottids (segments)

Neodermis allows worm to avoid Neodermis allows worm to avoid host’s immune systemhost’s immune system

Rely almost entirely on anaerobic Rely almost entirely on anaerobic respirationrespiration

Muscular, nervous, and Muscular, nervous, and protonephridial system is similar to protonephridial system is similar to that of turbellarians and trematodesthat of turbellarians and trematodes

ReproductionReproduction Strobilation occurs at neck regionStrobilation occurs at neck region

Each proglottid has a miniature reproductive systemEach proglottid has a miniature reproductive system During copulation, cirrus is everted and inserted into gonoporeDuring copulation, cirrus is everted and inserted into gonopore

When one worm is presentWhen one worm is present Self fertilize using one proglottidSelf fertilize using one proglottid Serf fertilize between two proglottidsSerf fertilize between two proglottids

When two or more worms are presentWhen two or more worms are present Cross fertilizeCross fertilize

Worms have proglottids that are in different stages of Worms have proglottids that are in different stages of sexual maturitysexual maturity Eggs constantly being producedEggs constantly being produced

Mature (gravid) proglottids break off from strobila and are Mature (gravid) proglottids break off from strobila and are passed in fecespassed in feces

Life CyclesLife Cycles Usually two or more hostsUsually two or more hosts

Definitive host always a vertebrateDefinitive host always a vertebrate

Aquatic and terrestrial life cyclesAquatic and terrestrial life cycles

DiphyllobothriumDiphyllobothrium is a fish tapeworm that can infect humans is a fish tapeworm that can infect humans Eggs in feces are deposited in waterEggs in feces are deposited in water Hatch into a ciliated, swimming oncosphere larva (has hooks)Hatch into a ciliated, swimming oncosphere larva (has hooks) Oncosphere is ingested by a copepodOncosphere is ingested by a copepod Oncosphere moves to hemocoel of copepod, sheds ciliated Oncosphere moves to hemocoel of copepod, sheds ciliated

epidermis, replaces with neodermis, and develops into a epidermis, replaces with neodermis, and develops into a procercoid larvaprocercoid larva

Fish eats copepodFish eats copepod Procercoid migrates from gut of fish to muscle, and transforms Procercoid migrates from gut of fish to muscle, and transforms

into a juvenile called a plerocercoid (metacestode)into a juvenile called a plerocercoid (metacestode) Development is completed in the gut lumen of a fish-eating Development is completed in the gut lumen of a fish-eating

vertebrate after ingestion of infected muscle tissuevertebrate after ingestion of infected muscle tissue

TaeniaTaenia is a terrestrial is a terrestrial tapeworm that infects tapeworm that infects domestic animals and domestic animals and humanshumans

Can reach 20 m but is Can reach 20 m but is typically 3 to 5 mtypically 3 to 5 m

LifecycleLifecycle Eggs are removed in fecesEggs are removed in feces Animal ingests eggs and Animal ingests eggs and

oncosphere bores through oncosphere bores through intestinal wall and intestinal wall and migrates to skeletal migrates to skeletal musclemuscle

Oncosphere develops into Oncosphere develops into a cysticercus (another a cysticercus (another metacestode w/ inverted metacestode w/ inverted scolex)scolex)

Development is completed Development is completed in the gut lumen of a in the gut lumen of a vertebrate after ingestion vertebrate after ingestion of infected muscle tissueof infected muscle tissue

Tapeworm infections cause Tapeworm infections cause diarrhea, weight loss, and lethargydiarrhea, weight loss, and lethargy

Occasionally humans accidentally Occasionally humans accidentally serve as an intermediate host, by serve as an intermediate host, by becoming infected with a becoming infected with a cysticercuscysticercus EchinococcusEchinococcus is often responsible for is often responsible for

thisthis

Cysticercus ends up in lung, liver, Cysticercus ends up in lung, liver, heart, brain, etc.heart, brain, etc.

Swells upSwells up

Known as a hydatid or hydatid cystKnown as a hydatid or hydatid cyst

Must be removed surgicallyMust be removed surgically

Some mortalitySome mortality