Phylum: Platyhelminthes
Class: Cestoda
By: Mr. “Conferences” Chapman

Cestoda
Class Cestoda –
tapeworms.
Tapeworms are
parasites that live in
the digestive systems
of vertebrate animals.

Scolex
Proglottids

Body Structure
Scolex (head)
Proglottids (body
segments).
Strobillus - The entire
length of the tapeworm’s
body, excluding the
scolex.

These are real tapeworms.
Scolex
Proglottids

Since tapeworms live in the intestines
of their host, they must be able to
hold on to the intestinal wall. If they
don’t they will move out of the host’s
intestines with its wastes. A series of
four suckers and ring of hooks on the
scolex anchor the tapeworm to the
host’s intestines.
The photographs at the
left and right show the
suckers and hooks on
the scolexes of living
tapeworms.

Body Structures
Since tapeworms live in
the intestines of their
host, they must be able to
hold on to the intestinal
wall. If they don’t they
will move out of the host’s
intestines with its wastes.
A series of four suckers
Rostellum - ring of hooks
on the scolex anchor the
tapeworm to the host’s
intestines.

Although tapeworms exhibit cephalization, they
have no eyespots. They also have lost their
digestive system to evolutionary change.
Because they live in their host’s intestine, they are
surrounded by food. Molecules of food simply
diffuse into the tapeworm’s cells from its
environment.

Cestoda
Some tapeworms grow
quite long. One species
that parasitizes horses
has been known to attain
a length of 75 feet.

Cestoda
The length is determined
by the number of
proglottids that remain
attached to the body.
Mature proglottids break
off and pass with the
host’s feces.

Cestoda
Living inside a
digestive system can
be hazardous.
Digestive enzymes
would simply dissolve
most worms.
Tapeworms have a
waxy cuticle that
covers their
ectoderm. It is
impermeable to the
enzymes.

Cestoda
Flatworms are
hermaphroditic.
Each proglottid is one
complete reproductive
system.
In these illustrations you
can see both male and
female reproductive
structures.

Cestoda
Sexual reproduction
occurs when two
tapeworms align, side by
side, exchanging sperm
through the genital pore
(atrium).
Eggs and sperm usually
mature at different times
so that a tapeworm
doesn’t fertilize its own
eggs.
This insures genetic
variation.

Cestoda
When the eggs in a
proglottid are fertilized,
the proglottid is
considered “gravid”.

Tapeworms
When a gravid
proglottid is at the
end of the worm, it
breaks off and
wiggles out the
host’s rectum.
It then dries, splits
open and spills out
its eggs which are
injested by a new
host.

Cestoda
The red and yellow object drawn
on this photograph is a wooden
match stick to show the size of
proglottids that have broken free
from the body of the tapeworm.
If your dog has tapeworms, the
best way to detect them is to look
around its rectum for the dried
rice-like proglottids that get caught
in the dogs fur.

The END