phylum platyhelminythes. platyhelminthes ~ 20,000 extant species parasitic + free-living unsegmented...
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Phylum Platyhelminythes
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Platyhelminthes
~ 20,000 extant species Parasitic + free-living Unsegmented flatworms
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Platyhelminthes Triploblastic, acoelomate, bilaterally
symmetrical Incomplete gut; absent in some parasitic forms Cephalization of nervous system Protonephridia: excretion and osmoregulation Hermaphroditic
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Support
Hydrostatic skeleton
Elastic body wall
Body musculature
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Taxonomy
Class Turbellaria
Class Monogenea
Class Trematoda
Class Cestoda
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Class Turbellaria
– Free-living flatworms
– Most are aquatic
– Epidermis cellular and ciliated
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Feeding and digestion in Turbellaria Consume invertebrates (few herbivores and
omnivores) Locate food via chemoreception A few are symbiotic
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Turbellaria digestive system
Mouth, pharynx, intestine = incomplete gut Pharyngeal glands produce mucus and
proteolytic enzymes Digestion extracellular, then phagocytization
in intestine
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Turbellaria nervous system Sense organs
– Tactile receptors cover body - concentrated anteriorly
– Chemoreception = location of food– Statocysts = gravity detection and
orientation– Photoreceptors
Inverted pigment cup ocelli Negative phototaxis
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Turbellaria nervous system
Variable: simple net-like to cephalized & bilateral
Ladder-like NS = more recently evolved
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Class Monogenea
Monogenetic flukes (life cycle = one host)– Body covered by tegument– Oral sucker reduced or absent– Ectoparasitic (usually fish)
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Class Monogenea
Monogenetic flukes (life cycle = one host)– Eggs hatch into ciliated larvae = oncomiracidia– Mature and find host
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Class Trematoda
Digenetic flukes (multiple hosts)– Body with tegument– One or more suckers present– Internal parasite
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Fluke Digestive System Feed on host tissues and fluids (muscular
pharynx)– Or, material in host gut
One-way digestive tract: mouth, muscular pharynx, short esophagus, intestinal cecae
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Fluke Nervous System Ladder-like Cerebral ganglion Suckers with tactile receptors (bristles
and spines)
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Sexual repro flukes
Hermaphroditic Mutual cross fertilization Male structures
– Variable testes Monogenetic = many Digenetic = two
– Sperm-to sperm duct, copulatory apparatus, eversible cirrus
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Sexual repro flukes Female Structures
– Ovary to oviduct to ootype– Oviduct joined by vitelline duct– Seminal receptacle = blind pouch off of
oviduct– Single uterus sometimes modified as vagina
near female gonopore
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Fluke reproduction Mutual cross-fertilization Sperm stored in seminal receptacle Eggs - oviduct to ootype then fertilized r-selected strategy (high fecundity)
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a – acetabulum d - vitelline ducts f - vitelline follicles o - oral sucker oe – oesophagus oo – ootype ov – ovary ph – pharynx sr - seminal receptable t – testis u - uterus
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Fluke life-cycles
Monogenetic– One host– Mostly external parasites of fish
Digenetic– Two or more hosts– Mostly internal parasites
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Fluke life-cycles: Chinese liver fluke
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Fluke life-cycles
Digenetic Fasciola = sheep liver fluke– Multiple hosts– Internal parasite of vertebrates– Intermediate host usually gastropod
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Fluke life-cyclesSchistosoma mansoni
Schistosomiasis = disease with problems from egg production, fevers, eggs lodged in various tissues
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Schistosomiasis
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Schistosoma spp. cause swimmer’s itch
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Class Cestoda
Tapeworms– Internal parasite– Body with tegument– Body with anterior scolex, short neck and
proglottids– No digestive system
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Tapeworms = cestodes Locomotion
– Sedentary: adult on host intestinal wall– Capable of muscular undulations
Attachment– Scolex– Anterior with hooks or adhesive pad
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Tapeworm digestion
No mouth, no digestive tract
Nutrients absorbed across tegument
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Tapeworm Nervous System
Cerebral ganglion; nerve ring in scolex Each proglottid has additional ganglia;
connect to longitudinal nerve cords Sensory organs reduced, tactile receptors in
scolex
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Sexual Repro: tapeworms
Hermaphroditic Mutual cross-fertilization Self-fertilization in some
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Proglottids
– Numerous testes along margins– Collecting tubules to coiled sperm duct – Vas deferens to genital pore
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Proglottids
– Two ovaries– Uterus = blind sac
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Tapeworm sex and fertilization Cirrus of each mate inserted into genital pores Sperm stored, eggs fertilized in oviduct Capsule material and yolk cells stored in uterus When mature, proglottids break free
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Beef Tapeworm Life Cycle
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Pork Tapeworm Life Cycle