Download Phylum Platyhelminthes

Kingdom Animalia
Subkingdom Eumetazoa
Bilateria
Phylum Platyhelminthes
Professor Andrea Garrison
Biology 3A
Illustrations ©2014 Cengage Learning unless
otherwise noted
Phylum Platyhelminthes
• Flat worms (platy = flat;
helminth = worm)
• Freshwater, marine,
moist soil, parasitic
• Triploblastic
• Protostomes
• Bilateral
w/cephalization
• Body dorsal-ventrally
flattened
Dugesia sp.
Platyhelminthes; photo by Eduard Solà;
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Phylum Platyhelminthes
• Organ systems
• Acoelomate
– Organs embedded in
mesoderm
Platyhelminthes
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Organ systems
• Incomplete Y-shaped gut
• Ladder-like nervous
system w/2 anterior
ganglia
• Reproductive system well
developed
– Hermaphroditic
– Sexual
– Asexual (fission)
• Excretory system
– Flame cells for osmoregulation
Platyhelminthes
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Phylum Platyhelminthes
• No respiratory or
circulatory systems
– Diffusion
• Body very thin
– No skeletal system
• 2-3 muscle layers in body
wall
– Circular, longitudinal,
sometimes oblique
Pseudobiceros bedfordi. Coral Sea
Platyhelminthes; photo by Richard Ling; http://creativecommons.org/licenses/by-sa/2.0/deed.en
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Phylum Platyhelminthes
• 4 classes
– Turbellaria – free living
– Trematoda – endoparasites
– Monogenoidea – ectoparasites on fish; no further
discussion
– Cestoda – endoparasites
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Class Turbellaria
• Free living
• Most marine
• Epidermis produces cilia
and mucus
• Locomotion
– Glide on mucus using muscles
and cilia
– Swim via undulating muscle
movements
Dugesia sp.
• Chemo- and tactile sensors
all over body
• Ocelli
– Light sensitive
Platyhelminthes; top photo by Eduard Solà;
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Class Turbellaria
• Digestive tract
– Mouth in center of ventral
surface
– Pharynx leads to Y-shaped
gut
• Varying degrees of branching
– Wrap body around prey
– Pharynx sucks up bits of food
– Intestine releases digestive
enzyme for extracellular
digestion
– Phagocytes in gastrodermis
engulf food
– Digestion completed inside
cells of gastrodermis
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Class Turbellaria
• Reproduction
– Sexual
• Copulate w/ another
individual
• Both fertilized by the
other
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Classes Trematoda & Cestoda
• Parasitic flatworms
Platyhelminthes
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Parasitic Lifestyle
• Parasitism
– special physical/nutritional relationship
(symbiosis) where one organism benefits and the
other is harmed
• What makes a “good” parasite?
– Don’t kill host
• No place else to live
• May weaken host
– Adaptations for living on/in host
– Often have elaborate life cycles
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Adaptations for Parasitism
• Don’t kill host directly
• Hooks/suckers for attachment
• Extensive reproductive system
– ↑ chances of offspring surviving
• Endoparasites
– Glands for penetrating tissues and/or encysting when
environment not good
– Intestinal parasites
• Tough integument
• Simple digestive tract
– Life cycles with many hosts
Platyhelminthes
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Parasitic Life Cycle
• Often multiple hosts
– Hosts may be from very different phyla
– Each stage of parasite life cycle often require very
specific genus or species of host
• Definitive host
– Parasite reaches final stage of development
– Sexual reproduction occurs here
• Intermediate host(s)
– Various stages of the parasite life cycle live in these
hosts
– May be the vector of transmission to final host
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Preventing Parasitic Diseases
• Can treat parasitic diseases like liver flukes,
trichinosis
– Done as the disease arises in the population
• Prevent parasitic diseases by
preventing/avoiding presence of the
intermediate hosts
– Far better for human health
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Class Trematoda
• Flukes
• Endoparasites; liver, blood,
lungs, gut of vertebrates
• Multihost life cycle
• Poorly developed sense
organs
• 2 suckers for attachment
Opisthorchis sinensis (=Clonorchis sinensis,
Chinese liver fluke)
– Oral and ventral
• Mouth at anterior end
• Gut with 2 branches
Platyhelminthes
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Class Trematoda – Chinese Liver Fluke
• Common in Asia
• Definitive hosts
– humans, cats, dogs, pigs
• Hermaphroditic
• Cause: eating raw or
undercooked fish, crab
• Can severely damage
liver (cirrhosis)
Opisthorchis sinensis (=Clonorchis sinensis,
Chinese liver fluke)
Platyhelminthes
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Class Trematoda – Chinese Liver Fluke
Platyhelminthes; http://www.cdc.gov/parasites/clonorchis/biology.html
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Class Trematoda – Blood Flukes
• 3 Schistosoma sp.
• Disease = schistosomiasis
– Major infectious disease worldwide
– Cause: working or swimming in infested water
• Definitive hosts
– Humans, dogs, cats, rodents, pigs, horse and goats
• Blood flukes not hermaphroditic
– Male much larger
– Female smaller and lives in grove on ventral surface of
male
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Class Trematoda – Schistosomiasis
Platyhelminthes: http://www.cdc.gov/parasites/schistosomiasis/biology.html
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Class Trematoda – Schistosomiasis
• Swimmer’s itch (cercarial dermatitis or
Schistosoma dermatitis)
– If aquatic larval stage burrows into host of wrong
species, it will die
– Humans may have an allergic reaction to the dead
parasite
• Rash, itching
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Class Cestoda
• Tapeworms
• Endoparasites;
intestines of vertebrates
• Multihost life cycle
• No sensory organs
– Do have sensory
receptors in integument
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Class Cestoda
• No gut
– External body surface
covered with
microscopic projections
• Enlarge surface area for
absorption
• Body with proglottids
– Repeated segments of
reproductive structures
– Hermaphroditic
– Thousands of fertilized
eggs in each
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Class Cestoda
• Scolex at anterior end
– Hooks and suckers for
attachment to intestinal
wall
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Class Cestoda – Life Cycle
• At least two hosts
– Definitive host is vertebrate
– Intermediate host may be invertebrate or vertebrate
• Infections usually have few symptoms
– One species can migrate to brain and cause seizures
• Taenia sp.
– Eating undercooked beef or pork
– Crowded, unsanitary conditions
Platyhelminthes
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Class Cestoda – Taenia sp.
Platyhelminthes; http://www.cdc.gov/parasites/taeniasis/biology.html
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Class Cestoda – Echinococcus
• Echinococcus granulosis
– Definitive host – dogs eat infected meat raw
– Intermediate host – sheep, goats, swine, cattle,
horses, camels
• Larvae migrate to organs (esp. liver, lungs)
– Humans in contact with dogs may accidentally
ingest eggs
• Hydatidosis
• Damage to liver, lungs, heart, bones
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Class Cestoda – Echinococcus
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