Flatworms are one of 14 worm phyla.
“Worm” grouping has no phylogenetic significance
(50)
(1,050)
(7)
All vermiform,
Bilateral symmetry
With no legs,
No exoskeleton
(15)
(9)
(15) (50)
(12)
(20)
Peanut worms
Horsehair worms
Round worms
Proboscis worms
Spaghetti worms
Inn Keeper worms
(6)
Class Monogenea
Class Turbellaria
>3,000 free-living spp
some commensal
a few parasitic forms
Aquatic, few on land
Body architecture adapted
to a free-living lifestyle
Class Trematoda: flukes
~ 400 spp
mostly ectoparasites of
fish, amphibians.
Feed on blood, mucus..
Anterior and posterior
ends for clinging,but life
cycle remains simple, with
a single free living larval
stage
4 principal types of flatworms
divided into 4 taxonomic Classes
P
haptors
> 6000 spp of endoparasites (liver, lungs, blood, muscles)
Body and life cycle adapted to parasitic existence.
A
Oral sucker
Ventral sucker
Characteristics of the Phylum
Class Cestoda: tapeworms
> 3500 spp of endoparsites, almost all intestinal parasites
with highly specialized body and life cycle.
Bilateral symmetry
Triploblastic
scolex
9 ft tapeworm from human host
Largest in sperm whale was over 30 meters long
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Characteristics of the Phylum
Bilaterally symmetry
Triploblastic
Acoelomate
Characteristics of the Phylum
Bilaterally symmetrical
Triploblastic
Unsegmented
Acoelomate
Organ Systems
video
Excretory System
W/ Ultrafiltration and selective absorption
Characteristics of the Phylum
Bilaterally symmetrical
Triploblastic
Unsegmented
Acoelomate
Organ Systems
Complex reprod. System
Regenerative capacities
Paratomy
Architomy
Budding
Pluripotent stem cells (neoblasts) capable of producing all
cell types account for great ability to heal and regenerate
Negligible senescence: no measurable reductions in reproductive or
functional capability with age (telomerase?)
Flatworms, sturgeon, tortoises
Most Widely Accepted Phylogeny of the Major
Flatworm Classes
(endoparasitic)
Negligible Senescence : telomerase?
Rougheye rockfish (Sebastes aleutianus) — 205 years[5][6]
Aldabra Giant Tortoise—255 years
Galapagos tortoisres 280 +
Lobsters are believed to live 100 or more years.[7]
Hydras are observed to be biologically immortal.[8]
Sea anemones generally live up to 60–80 years.[9]
Freshwater pearl mussel—210–250 years[10][11]
Ocean Quahog clam—405 years[12]
Monogenea
(ectoparasitic)
Trematoda
Neodermata
Cestoda
(endoparasitic)
Turbellaria
-- Parasitic groups considered to be monophyletic and
constitute a grouping known as the Neodermata
Synapomorphies: new skin, obligate parasitism,
protonephridia from two cells
No synapomorphies for the phylum; thought to be polyphyletic
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Problems Posed by Endoparasitic Existence
In all Neodermata, epidermis is shed, and replaced by
a syncitial tegument.
• Reproduce and get embryos out of the host
• Contact new, appropriate host and obtain entrance
• Locate appropriate environment in the new host
• Maintain position in the host, withstand often
anaerobic conditions and attack by immune system
• Avoid killing the host, at least until
reproduction has been completed
Advantages to having
a tegument?
The body wall is a tegument with extensive
microvillar surface area
Monogenean tegument
Cestode tegument
Class Cestoidea
Subclass Eucestoda: the tapeworms
Intestinal
Parasites,
commonly on
vertebrates
hermaphroditic
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Cystecercoids can accidentally end up in other
parts of a body, especially in accidental hosts
such as humans when they ingest eggs
• Relatively simple
• Passive dispersal
• Reproduction is
primarily sexual
oncosphere
Class Trematoda:
Dead End
all endoparasites in blood, liver, gut
distinguished by presence of ventral sucker
(acetabulum), mouth and highly branched G-V Cavity
Usually 2 intermediate hosts, at least one being a
mollusc; the final host is a vertebrate
Class
Trematoda:
Common in China, Korea
Japan, where practice
of eating uncooked
fish is common
Ex.
Chinese
Liver
Fluke
Adults live in the liver
and bile passages
Class Trematoda:
Schistosoma mansoni
A snail
is usually
the
intermediate
Host
Clonorchis sinensis
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Class Trematoda:
Schistosome life cycles
are unusual
in several ways
-- One intermediate host
Eggs pass through blood vessel
into gut, and out….
Or they lodge in nervous tissue,
muscles, other organs, causing
excrutiating pain &tissue damage.
-- Have Separate Sexes!
-- Adults live within blood
vessels, feed on blood
Schistosome Egg and spine
Class Trematoda:
Schistosome life
cycles are unusual
in several ways
Separate sexes: dioecious
Picture of the
Happy couple
3 species mainly
invade humans
General Pathology
S. mansoni, S japonicum
•  Acute schistosomiasis: fever, nausea, cough etc., and
granuloma formation after female begins to lay eggs
S. japonicum
S. haematobium
Of 200 million infected approximately 120 million show symptoms. The
mortality rate is about 2.5% but more frequent in children (5 million deaths,
200K in Sub-Saharan Africa alone)
S. mansoni
•  Chronic Schistosomiasis: could be years later
intestinal schistosomiasis: granulomatous inflamation
around eggs; colonic polyps, especially in Egypt.
hepatosplenic schistosomiasis: inflammation around
eggs trapped in liver, leading to fibrosis,
cirrhosis
S haematobium:
parasites in the bladder and ureter, can lead to
calcification, cancer….”urinary schistosomiasis”
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