
Flatworms
› Phylum Platyhelminthes
› Class Turbellaria, Cestoda, Trematoda, Monogenea
› Families 102 variations

(Pseudoceros bimarginatus)
Roundworms
› Phylum Nematoda
› Class
Adenophorea, Secernentea,
› Families A LOT
(Enterobius vermicularis)

Flatworms:
› Scientists don’t really know
› Parasitic flatworms
probably evolved from
free-living animals

Roundworms:
› Scientists believe the
roundworms lived
somewhere in the
Proterozoic Era (1+ billion
years ago)

Flatworms:
Bilaterally symmetrical
 3 germ layers – ecto-, meso-,
endo-, -derms that press
against each other
 Gastrovascular cavity-gut with
1 opening
 Acoelomates- lack a hollow
body cavity


Roundworms:
Bilaterally symmetrical
 Pseudocoelomates-have a
hollow fluid filled cavity lined
by mesoderm outside and
endoderm inside



Flatworms:
Varying structural systems
including proglottids or
sections, tegument or an outer
layer of proteins and
carbohydrates

Roundworms:

Hydrostatic skeleton

Flatworms:
Turbellarians, monogeneans,
and trematodes have a
digestive system, but cestodes
don’t
 Mouths are on the front or side
of the head
 Turbellarians are always nonparasitic, while monogeneans,
trematodes and csetodes are
parasites, usually found on or
inside an organism
 Flatworms eat small worms,
insects and microscopic
matter


Roundworms:
Can be herbivores, omnivores,
or carnivores
 Mouth to pharynx to intestine
to anus


Flatworms:
No formal circulatory system
 Cilia & muscles


Roundworms:
Use muscles and the fluid in
their pseudocoelum to make
a “hydrostatic skeleton”
 Aquatic worms use these
muscles to swim, while
terrestrial worms thrash around
 No formal circulatory system


Flatworms:
No formal respiratory system
 Being extremely thin,
flatworms can exchange
gases, mainly oxygen and
carbon dioxide, directly with
their environment through
diffusion


Roundworms:
No formal respiratory systems
 Oxygen is diffused through the
environment


Flatworms:
Excretion & eating both use
the same opening
 Protonephredia and flame
cells regulate water balance
 Water balance or
osmoregulation is
maintained by
protonephridia, which
terminate in specialized
flame cells



Roundworms:
Fecal matter exits through the
anus

Flatworms:
› Sexual:
 Fertilization is internal
 Eggs are ectolecithal;
the ova are provided
with yolk cells and the
egg mass is surrounded
in a capsule.
› Asexual
 Very frequent
 Turbellarians reproduce
by fragmentation or
binary fission.

Roundworms:
› Sexual:
 Males have testes,
where females have
ovaries
 Fertilization is internal

Flatworms:

Roundworms:
› Organizaton of ganglia is a
central region of nerve
processes.
› Consist of a large
circumesophageal
commissure -nerve ring.
› Nerve cords are usually
› There are commissures
arranged in symmetrical
pairs.
that interwoven the ventral
nerve cord with the lateral
or dorsal nerves
› Lateral nerves are primarily
sensory.
› The dorsal and ventral
nerve cords are motor.

Flatworms:
› They are studied for their
regenerative abilities.
› Cause pathological
troubles or difficulty in
marine ornamental
fishes.

Roundworms:
› Parasitic
adenophoreans aid
plants in receiving
diseases.
› cause dehydration and
loss of nutrition in plants.
› Help to cycle carbon
and nitrogen





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

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Essortment Web site: http://www.essortment.com/all/flatwormroundwo_rmhm.htm
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http://www.mcwdn.org/Animals/Flatworm.html
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STATE UNIVERSITY Web site: http://www.personal.psu.edu/users/t/r/trp2/flatworms.html
"Turbellarians: Turbellaria." Grzimek's Student Animal Life Resource. Ed. Catherine Judge
Allen, Arthur V. Evans, Melissa C. McDade, Neil Schlager, Leslie A. Mertz, Madeline S.
Harris, et al. Vol. 9: Corals, Jellyfishes, Sponges, and Other Simple Animals. Detroit: UXL,
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2009 http://go.galegroup.com/ps/start.do?p=GVRL&u=vern39182
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Judge Allen, Arthur V. Evans, Melissa C. McDade, Neil Schlager, Leslie A. Mertz,
Madeline S. Harris, et al. Vol. 9: Corals, Jellyfishes, Sponges, and Other Simple Animals.
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SCHOOL. 11 Apr. 2009 http://go.galegroup.com/ps/start.do?p=GVRL&u=vern39182
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