Chapter 14Chapter 14

Acoelomate Bilateral AnimalsAcoelomate Bilateral Animals

PLATYHELMINTHESPLATYHELMINTHES

Overall CharacteristicsOverall Characteristics

AcoeolomateAcoeolomate Only one internal spaceOnly one internal space

Bilateral Symmetry Bilateral Symmetry due to due to cephalizationcephalization

Triploblastic Three germ layers (formed during embryonic Three germ layers (formed during embryonic

development)development) Middle mesodermal layer: Middle mesodermal layer: parenchymaparenchyma

Platyhelminthes: the classesPlatyhelminthes: the classes

1. 1. TurbellariaTurbellaria free living flatwormsfree living flatworms

2. Monogenea2. Monogenea Most are ectoparasitesMost are ectoparasites

3. 3. TrematodaTrematoda flukesflukes All are endoparasitesAll are endoparasites

4. 4. CestodaCestoda tapewormstapeworms All are endoparasitesAll are endoparasites

I. Form and FunctionI. Form and Function Most have Ciliated Most have Ciliated

epidermisepidermis Epidermis (Tegument)Epidermis (Tegument)

CiliatedCiliated syncytial syncytial

(multinucleated) (multinucleated) Basement layerBasement layer

separating epidermal from separating epidermal from organ layersorgan layers

contains contains rhabditesrhabdites• Produce Produce mucousmucous

Muscle fibers below Muscle fibers below basement layerbasement layer

Dual-gland Dual-gland adhesive adhesive organs (turbellarians)organs (turbellarians)

Viscid gland = stickViscid gland = stick Releasing gland = Releasing gland =

releaserelease 1 Anchor cell1 Anchor cell

A. Nutrition and Digestion A. Nutrition and Digestion

Mouth, Mouth, pharynxpharynx & & intestine (except intestine (except cestodes)cestodes)

gastrovascular cavitygastrovascular cavity branchingbranching

MostlyMostly free-living & free-living & carnivorous carnivorous

detect prey by detect prey by chemoreceptionchemoreception Like smelling them!Like smelling them!

Extracellular digestionExtracellular digestion enzymesenzymes

Intracellular digestionIntracellular digestion phagocytosisphagocytosis

B. Excretion & OsmoregulationB. Excretion & Osmoregulation

C. Nervous SystemC. Nervous System BrainBrain

Anterior GangliaAnterior Ganglia Bundle of neuronsBundle of neurons

Longitudinal Nerve cordsLongitudinal Nerve cords Sensory: collect info from environmentSensory: collect info from environment Motor: actionMotor: action Association: linkAssociation: link

D. Sense OrgansD. Sense Organs

5 sense organs5 sense organs Mechanoreceptors - tactile (touch)Mechanoreceptors - tactile (touch) Chemoreception - taste / smell, mates?Chemoreception - taste / smell, mates? RheoceptorsRheoceptors (H (H22O flow)O flow) Statocysts - balanceStatocysts - balance Ocelli - simple visionOcelli - simple vision

TurbellariaTurbellaria

PolyphileticPolyphiletic (p. 302) (p. 302) Simple life cyclesSimple life cycles .5 to 50cm iin length.5 to 50cm iin length MidventralMidventral mouth or mouth or

proboscis (planaria)proboscis (planaria) Not at anterior (head) endNot at anterior (head) end

Muscular waves & or Muscular waves & or ciliary ciliary locomotionlocomotion

Gut varies from none to Gut varies from none to highly branched highly branched (correlates with size)(correlates with size)

Order Order AcoelaAcoela (primative marine (primative marine flatworms) flatworms) only mouth, only mouth, no gastrovascular cavity!no gastrovascular cavity!

Amazing Amazing regenerative abilities- abilities- planaria planaria developmental studiesdevelopmental studies

E. ReproductionE. Reproduction

Reproductive SystemReproductive System

III. Class Trematoda (flukes)III. Class Trematoda (flukes)

ParasiticParasitic Vertebrate host and Vertebrate host and

invertebrate Intermediate invertebrate Intermediate hosthost

Leaf-likeLeaf-like Suckers (two) & or hooksSuckers (two) & or hooks Well developedWell developed

alimentary canalalimentary canal Nervous system (non-sensory)Nervous system (non-sensory) Excretory systemExcretory system Reproductive systemReproductive system

A. SubclassA. Subclass DigeneaDigenea Mollusk intermediateMollusk intermediate Human definitive hostHuman definitive host Pass via excreta to Pass via excreta to

HH22OO Infect many body Infect many body

systemssystems• DigestiveDigestive• RespiratoryRespiratory• UrinaryUrinary• reproductivereproductive• Circulatory systemCirculatory system

B. Liver Fluke• 1. All trematodes are

parasitic flukes.

• 2. Most adults are endoparasites of vertebrates.

• Most sporocysts are endoparasites of invertebrates.

• 3. They resemble some Turbellaria but the tegument lacks cilia in adults.

• 4. Adaptations for parasitism include:

a. penetration glands, b. glands to produce cyst

material, c. hooks and suckers for

adhesion, and d. increased reproductive

capacity!!!

• 5. Sense organs are poorly developed.

250,000

Fluke life cycle Clonarchis (liver fluke)Clonarchis (liver fluke)

More Egg (Shelled miracidium)Egg (Shelled miracidium) MiracidiumMiracidium (free (free

swimming larva) swimming larva) penetrates first invertebrate penetrates first invertebrate hosthost

SporocystSporocyst forms in host forms in host ((asexualasexual reproduction) reproduction)

RediaeRediae from sporocyst from sporocyst which also reproduce which also reproduce asexuallyasexually to create.. to create..

Cercariae Cercariae which emerge which emerge from the intermediate host from the intermediate host to become..to become..

MetacercariaeMetacercariae which infect which infect another intermediate or another intermediate or final final vertebratevertebrate host and host and mature, usually after mature, usually after ingestioningestion

Eg. Chinese liver fluke Eg. Chinese liver fluke (monoecious)(monoecious)

MultiplicationMultiplication1 miracidium to 250,000 1 miracidium to 250,000

cercariae!!!cercariae!!!

C. Schistosoma (blood flukes)(blood flukes) Sexual dimorphism Sexual dimorphism

(dioecious)(dioecious)• Male larger than femaleMale larger than female

SnailSnail Human (penetrates skin)Human (penetrates skin) 200 - 300 million people 200 - 300 million people

infected globallyinfected globally Multiple organ infectionMultiple organ infection Sometimes fatalSometimes fatal No rediae intermediateNo rediae intermediate Cirrhosis of the liver (eggs)Cirrhosis of the liver (eggs) Image

Lung FlukesLung Flukes SnailsSnails Crabs and crayfishCrabs and crayfish Vertebrates (humans)Vertebrates (humans)

Leucochloridium paradoxum paradoxum

snails and birdssnails and birds sporocystsporocyst

Be careful what Be careful what you drink, eat, & you drink, eat, & where you wade!where you wade!

V. ClassV. Class Cestoda Cestoda Tapeworm

Taenia saginatusTaenia saginatus (beef) (beef) Taenia solium (pork)Taenia solium (pork)

FormForm Gutless wonders!wonders! Microtriches (tegument)Microtriches (tegument) Scolex Scolex Germinative zoneGerminative zone ProglottidsProglottids (Strobila (Strobila

chain)chain) Life CycleLife Cycle

Monoecious Monoecious Self fertilization (or not)Self fertilization (or not) Gravid proglottidGravid proglottid

Shelled larvaeShelled larvae Consumed by intermediateConsumed by intermediate Muscle cystsMuscle cysts Bladder cysts (invaginated Bladder cysts (invaginated

cysticercus)cysticercus) Hydatid cyst (dog Hydatid cyst (dog

tapeworm)tapeworm) Uncooked meatUncooked meat Definitive host consumes Definitive host consumes

intermediate hostintermediate host Cysticercosis (ingestion of Cysticercosis (ingestion of

eggs or proglottids)eggs or proglottids)

Class Cestoda Class Cestoda • 1. Tapeworms have a unique 1. Tapeworms have a unique

flattened and segmented flattened and segmented shape compared to other shape compared to other flatworms. flatworms.

• 2. Each trailing segment is a 2. Each trailing segment is a proglottid proglottid containing a set of containing a set of reproductive organs. reproductive organs.

• 3. The entire surface of 3. The entire surface of cestodes is covered with cestodes is covered with projections similar to microvilli projections similar to microvilli seen in the vertebrate small seen in the vertebrate small intestine; intestine; these these microtriches microtriches increase the surface area for increase the surface area for food absorptionfood absorption. .

• 4. Nearly all are monoecious. 4. Nearly all are monoecious.

• 5. They lack sensory organs 5. They lack sensory organs except for modified cilia. (Fig. except for modified cilia. (Fig. 14-17) 14-17)

• 6. The 6. The scolex scolex is a holdfast is a holdfast head portion with suckers and head portion with suckers and hooks. hooks.