chapter 14 acoelomate bilateral animals platyhelminthes
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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
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
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.
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