Phylum Platyhelminthes
Classes:
Flatworms (Turbellaria)
Flukes (Trematoda)
Tapeworms (Cestoda)
Monogeneans
1
Phylum Platyhelminthes
They
are Acoelomates
because they lack body
cavity (Coelom).
This
gives them a flat
body structure (Flat
worms)
2
Phylum Platyhelminthes
Flatworm Body Plans


3
Exhibit bilateral symmetry, acoelomate, and are
triploblastic
Parenchyma tissue
Phylum Platyhelminthes
Taxonomic Summary
4
Phylum Platyhelminthes
5
Phylum Platyhelminthes
CHARACTERISTICS






6
BILATERAL SYMMETRY
THREE GERM LAYERS (TRIPLOBLASTIC)
CENTRALIZED NERVOUS SYSTEM
SIMPLE EXCRETORY SYSTEM
COMPLEX REPRODUCTIVE SYSTEM
SIMPLE DIGESTIVE SYSTEM
Phylum Platyhelminthes
Reproduction



7
Almost all are simultaneous
hermaphrodites
Parasitic species (flukes and
tapeworms) have complex
lifecycles, with various hosts
and several different larval
stages
Incredible powers of
regeneration
Phylum Platyhelminthes
Nervous System


Free-living species usually have a
well-developed sensory system
Parasites generally have less
elaborate systems.
WHY?
8
Phylum Platyhelminthes
Class Turbellaria

Most are free–living,
tiny and
inconspicuous
–
Primarily marine and
freshwater
–
e.g Planaria
Free-living
Flatworm
9
Phylum Platyhelminthes
Digestion and Excretion
10

Mouth is usually located
at the anterior end or
mid-body on ventral
surface

Excretory system
– Contains flame
bulbs known as
flame cell.
Phylum Platyhelminthes
Regeneration

11
Many species posses remarkable powers of
regeneration and repair wounds
Phylum Platyhelminthes
Turbellarian Lifestyles
12

Most are benthic

Posses several nerve cords with a centralized
ganglia (brain)
Phylum Platyhelminthes
Reproduction

Reproduction occurs
with the reciprocal
exchange of sperm.

Fertilized eggs are
released and usually
develop directly into
flatworms
–
13
Muller's larva
Phylum Platyhelminthes
Class Cestoda (Tapeworms)

Defining
characteristics
–
–
–
–
–
–
14
Scolex
Proglottids
All parasitic
E.g Taenia saginatta
(beef tapeworm)
Taenia solium
(pork tapeworm)
Phylum Platyhelminthes
Proglottids

15
Proglottids
– Each animal can be
3,000 – 4,000 per
animal
– Amazing reproductive
output
– Each may contain
several ovaries and
1,000 distinct testes
Phylum Platyhelminthes
16
Phylum Platyhelminthes
Class Trematoda (Flukes)
17

All are external and internal parasites of
other animals.

Leech-like bodies with a sucker at each
end.

Have a gut and well-developed
reproductive system, never segmented.

Blood flukes (Shistosomes),Liver flukes
(Fasciola) & Lung flukes (Paragonimus)
Phylum Platyhelminthes
Schistosomes (Blood Fluke)
18

Causes infection known as Schistosomiasis
(Formally Bilharziasis)

They are dioecious (Sexes are separted)

Adult males carry females in a gynaecophoric
canal.
Phylum Platyhelminthes
Schistosome species
19
Species
Snail
intermediate
host
Location
in host
veins
Type of
eggs spine
S. mansoni
Biomphalaria
Large
intestine
Lateral spine
S. japonicum
Onchomelenia
Small
intestine
Small round knob
S. haematobium
Bulinus
Urinary
bladder
Terminal spine
Phylum Platyhelminthes
Trematoda Lifecycles

20
The lifecycle is
complex with
up to 4 different
hosts and
several larval
types
Phylum Platyhelminthes
Life Cycle of Blood fluke
(Schistosomes)
Trematodes of Concern

Schistosomiasis
–
–
–
21
Deadly prominent disease in
many regions of the world
Bores into the skin of the
definitive host and travels in
the circulatory system to the
heart the lungs and the
kidneys where it feeds and
grows
Inflammation is caused by
eggs becoming trapped in the
hosts tissues

Chinese liver fluke
–
–
–
Lives in the bile duct of
humans, cats, and dogs
(1-2 cm.)
Goes through two
intermediate hosts
Infection occurs from
ingestion of raw fish
Phylum Platyhelminthes
Liver Fluke (Fasciola)

Causes fascioliasis or liver rot in sheeps and
dogs.
Major examples : F. Hepatica & F. Gigantica

Snail intermediate host- Lymnaea

22
Phylum Platyhelminthes
Life cycle of Liver fluke (Fasciola)
23
Phylum Platyhelminthes