Unsegmented Worms
Phylum Platyhelminthes
I. Unsegmented worms
A. = Worms that are not
divided into sections
externally & internally
B. E.g.
1. Phylum Platyhelminthes
aka flatworms
2. Phylum Nematoda
aka Roundworms
C. What is a coelom?
=
fluid-filled
body cavity
between
body wall
& digestive tract
Kinds of coelom
1. Acoelomate= no coelom
i.e. body cavity is
NOT fluid filled
Kinds of coelom
2.
Pseudocoelomate
= Fluid filled
body cavity
BUT
No mesentary
or
peritoneum
Kinds of coelom
3. Eucoelomate
=
True coelom
w/ mesentary
(holds gut in
place)
& peritoneum
(mesodermal
lining of body
cavity
D. Phylum Platyhelminthes
1. Class : Turbellaria – planarians
2. Class : Trematoda – flukes
3. Class : Cestoda – tapeworms
D. Phylum Platyhelminthes
Also Acoelomate:
• Phylum Nemertea – ribbon worms
• Phylum Gnathostomulidajaw worms
E. General Info re: Flatworms
1. = “platy” = flat
“helminth” = worm
2. Body structure
a. Size range 1 mm ------►
many meters (Cestoda)
b. Shape – flattened dorso-ventrally
c. Only several cell layers thick
E. General Info re: Flatworms
 Cells fill body cavity (not fluid)
F. Level of Organization
= organ system
G. Symmetry
•
•
bilateral
(has forward movement & cephalization)
I ‘m a little
bilateral
animal
too!
H. Habitat
• aquatic (freshwater
or marine)
• moist soil
• endoparasites of vertebrates
I. Feeding - Class Turbellaria
Planariansmostly
free-living
carnivore
or
scavengers
I. Feeding - Class Turbellaria
– Incomplete digestive
tract – one opening
(no anus)
– Mouth on ventral side
– Protrusible pharynx
– Gastrovascular cavity
(GVC)
– “Intestine” very
branched
– Enzymes digest food
I. Feeding - Class Trematoda
• Parasitic flukes
• endoparasites
of
vertebrates
• need only
minimal
digestive tract
• E.g. Human Liver fluke
I. Feeding – Class Cestoda
tapeworms
scolex
–Endo-parasites
–Scolex w/ hooks & suckers
–NO need for dig. tract
– absorbs nutrients from gut of host
suckers
J. Respiration
•
•
- via diffusion
(only a few cell layers thick)
K. Internal transport
•
via diffusion
Marine flatworm
L. Excretion – via diffusion
•
•
•
•
EXCEPTION:
planarians have
flame cells ( w/
flagella
that help move
waste to
excretory pores,
then out of the body
M. Response – (Nervous system)
1. Primitive brain – anterior ganglia
ganglion = cluster of nerve cells
2. Two Longitudinal nerves (the length of the
body)
3. Ladder-like cross-bridges of nerves
M. Response – (Nervous system)
M. Response – (Nervous system)
4. Sense organs: (flatworms)
a. Ocelli – eyespots / photodetectors
b. Auricles contain chemoreceptors (chemicals)
& thigmoreceptors (touch)
c. Statocysts – balance
d. Rheoreceptors – sense
direction of water current
N. Locomotion
- Planaria –
use cilia,
slime,
circular and
longitudinal
muscles
to GLIDE
– Trematoda,
Cestoda –
little motion
cilia
O. Reproduction
1. Asexual – Regeneration (Planaria only)
2. Sexual –
a. pattern = monoecious
(hermaphrodites)
b. cross- fertilization (swap sperm)
P. Ecological Roles
1. Scavengers/ predators – recycle nutrients
to ecosystem (Class Turbellaria)
2. Prey for fish & birds (Class Turbellaria)
3. Endo-parasites (cause disease)
(Class Trematoda & Class Cestoda)