2. Cestoda
• The Cestoda, or tapeworms, being a subclass of
parasitic flatworms, possess all the characteristics of
the phylum Platyhelminthes.
• The most striking difference between members of
this subclass and the class Trematoda is that
tapeworms lack a mouth and digestive tract.
3. Cestoda
• The Cestoda are the most highly specialized flatworm
parasites known. Adults of this subclass are
endoparasitic in the alimentary tract and associated
ducts of various vertebrates, including humans;
• the larvae, on the other hand, infect both
vertebrates and invertebrates.
• The life cycle requires one or two intermediate hosts,
in each of which the tapeworm undergoes a specific
developmental phase
4.
5. MORPHOLOGY
• The body of the
typical adult
eucestode consists
of three distinct
regions:
• scolex,
• neck,
• strobila
6. MORPHOLOGY
• The scolex, located at the
anterior end, is the
attachment terminal, the
morphology and dimensions
of which are key features in
identification of these
worms
• The neck, an unsegmented,
poorly differentiated region
immediately posterior to the
scolex, is generally the
narrowest part of the worm
7. MORPHOLOGY
• As new proglottids are
formed in the neck
region, they push the
older ones progressively
posteriad, creating a
chain of proglottids, the
strobila, that
constitutes the third
body region
8. MORPHOLOGY
• The asexual process of forming
segments is termed strobilation.
• As each proglottid is shifted posteriad,
its sexual reproductive system
matures progressively; hence, the
anteriormost proglottids have the
least developed reproductive systems,
while the more posteriorly the
proglottids are located, the higher
their level of development
• This progressive maturity of the
reproductive systems permits a loose
subdivision of the strobila into regions
of immature, mature, and gravid
proglottids
9. MORPHOLOGY
• In apolytic species, gravid proglottids
detach from the strobila and exit the
body of the host with fecal wastes.
• In anapolytic species, eggs are
released through a uterine (or genital)
pore directly into the host’s intestine
and, subsequently, also are discharged
to the exterior in feces.
• Most anapolytic tapeworms produce
protective, tanned eggshells.
10. MORPHOLOGY
Tegument
• Tegument (helminth) is a term in helminthology for the
outer body covering of members of the phylum
Platyhelminthes. The name is derived from a Latin word
tegumentum or tegere, meaning "to cover". It is
characteristic of flatworms including the broad groups of
tapeworms and flukes.
• The surface of the tapeworm tegument bears specialized
microvilli, known as microthrices (singular, microthrix),
which project from the outer, limiting membrane of the
tegument.
12. MORPHOLOGY
Parenchyma
• The space enclosed by the tegument except for the
portion occupied by reproductive organs,
osmoregulatory structures, muscle fibers, and
nervous tissued is filled with a spongy tissue known
as the parenchyma
• In live tapeworms, fluid fills the spaces between
parenchymal cells. Parenchymal cells are the
primary sites for synthesis and storage of glycogen.
• In live tapeworms, fluid fills the spaces between
parenchymal cells. Parenchymal cells are the
primary sites for synthesis and storage of glycogen.
•
13. MORPHOLOGY
Scolex
• To facilitate attachment to the host’s intestinal wall,
tapeworms utilize several types of structures on
their scolices, the most common of which are
suckers.
• Muscles in the scolex make possible the holdfast
action of this organ. The musculature of the scolex
consists of sets of crisscrossing fibers attached to
the inner surfaces of the suckers, enabling them to
contract
15. Nervous System
The cestode nervous system
is relatively complex. The
“brain,” located in the
scolex, is a rectangular or
circular arrangement of
nerve tissue varying in
complexity from a simple
ganglion to a combination of
several ganglia and
commissures
16. Reproductive Systems
The general pattern of the reproductive system of
cestodes resembles that of digenetic trematodes
except for the cul-de-sac uterus in some forms
(cyclophyllideans), the presence of a separate vaginal
canal, and often a laterally situated genital pore
17. Reproductive Systems
Male System
• The male reproductive system consists of from one to
many testes embedded in the medullary parenchyma of
each proglottid.
• Emanating from each testis is a single vas efferens; in
cases of multiple testes, the vasa efferentia unite to
form a common vas deferens, which is usually coiled.
• The distal portion of the vas deferens is modified as a
muscular cirrus, usually enclosed within a cirrus sac.
• In some species, the cirrus is equipped with spines that
hold the organ in place during copulation. The cirrus
everts through the male genital pore, which then opens
into the common genital atrium.
18. Reproductive Systems
Male System
• In most species there is an
enlarged area of the vas
deferens, the seminal vesicle,
for storage of sperm.
• When located within the cirrus
sac, it is designated an internal
seminal vesicle;
• located outside the sac, it is
termed an external seminal
vesicle.
• Some species possess both.
19. Reproductive Systems
Female System
• Ova are produced in a single, sometimes bilobed ovary.
• Following fertilization in the proximal portion of the
oviduct, the resulting zygote passes into a region of the
oviduct, the ootype, equipped with structures involved in
eggshell formation similar to those found in digeneans.
• A Mehlis’ gland surrounds the ootype and secretes into
it material essential to formation of the eggshell; a
single, common vitelline duct enters the oviduct in the
vicinity of the ootype.
20. Reproductive Systems
Female System
• The common vitelline duct is formed by the union of many
primary vitelline ducts arising from vitelline glands, which
vary in size and location according to species.
• Vitelline glands (collectively designated as the vitellaria)
may form a compact body or consist of numerous follicles
scattered throughout the medullary region of the
parenchyma.
• With few exceptions, secretions of the vitelline glands
contain shell precursors and provide nourishment for the
developing larva.
21. Reproductive Systems
Female System
• The vagina, a tubular organ
that joins the oviduct at the
level of Mehlis’ gland,
provides a passage for
sperm between the genital
atrium and the oviduct.
• Fertilization occurs in the
region where the vagina and
oviduct join. Sperm are
stored in an enlargement of
the vagina known as the
seminal receptacle.
22. Reproductive Systems
Female System
• The oviduct continues as the uterus, which, in some
tapeworms such as the anapolytic members of the order
Pseudophyllidea, opens to the outside of the proglottid
through a uterine pore.
• Eggs are produced continuously and are expelled
through this opening. In other species, including members
of the order Cyclophyllidea, the uterus is a blind sac in
which developing eggs accumulate; the uterus becomes
distended with eggs, filling the medullary region of the
proglottid.
23. Reproductive Systems
Female System
• The gravid proglottid eventually becomes detached from
the strobila and is discharged from the host. In some
tapeworms (Dipylidium, etc.), there is a modification of
uterus-egg interaction in which a much-reduced uterus,
upon receiving a specific number of eggs, begins pinching
off egg capsules, which eventually fill the medullary region
of the gravid proglottid.
• During copulation, the cirrus of one proglottid may be
inserted in the vagina of another proglottid of the same, or
another, worm
24. The Eggs
• The morphology of tapeworm eggs is important for
species identification. The following is a brief general
description of the basic parts of a typical egg
25. The Eggs
• The oncosphere, containing three pairs of hooks, is
encased in an inner envelope that is surrounded by
another membranous structure, the embryophore.
• A cellular zone known as the outer envelope lies
between the embryophore and the shell (or
capsule), usually the outermost covering of the egg.
26. The Eggs
Tapeworm eggs exhibit
certain variations
within this basic
pattern and are
classified into four
types:
1. pseudophyllidean (a),
2. dipylidean (b)
3. taenioid (c)
4. stilesian
27. The Eggs
Tapeworm eggs exhibit
certain variations
within this basic
pattern and are
classified into four
types:
1. pseudophyllidean (a),
2. dipylidean (b)
3. taenioid (c)
4. stilesian
28. The Eggs
The three types of
egg-forming tapeworms
that infect humans.
• (a) Pseudophyllidean, e.g.,
in Diphyllobothrium
latum.
• (b) Dipylidean, e.g., in
Hymenolepis nana.
• (c) Taenioid, e.g., in Taenia
solium.
29. LIFE CYCLE PATTERNS
Tapeworms that infect humans display one of two basic
life cycle patterns,
• one typical of members of the order
Pseudophyllidea,
• the other of members of the order Cyclophyllidea
30. LIFE CYCLE PATTERNS
Tapeworms that infect humans display one of two basic
life cycle patterns,
• one typical of members of the order
Pseudophyllidea,
• the other of members of the order Cyclophyllidea
