The document summarizes key aspects of four classes of flatworms - Turbellaria, Trematoda, Monogenea, and Cestoidea. It provides details on the life cycles and characteristics of Monogenea and Cestoidea. Cestoidea, or tapeworms, can be intestinal parasites in humans, with some examples given like the beef, pork, and fish tapeworms. The document outlines the tapeworm life cycle and morphology, including stages like proglottids and scolex.

1. INVERTEBRATES (Zool-02506)
3(2-1)
Presented by: Nabeel Tahir
M.Phil. Zoology
Class: ADP 5 Semester
Lecture: 8

2. PLATYZOA:PHYLUM PLATYHELMINTHES

3. CLASSIFICATION OF THE
PLATYHELMINTHES
• Class Turbellaria
• Class Trematoda
• Class Monogenea
• Class Cestoidea

4. Class Monogenea
• Only one generation in their life cycle.
• External parasites (ectoparasites) of
freshwater and marine fishes.
• Opisthaptor: large, posterior
attachment organ.
• Life Cycle: Adult monogeneans
produce and release eggs.
• Eggs attach to fish gill by one or more
sticky threads.
• Oncomiracidium: a ciliated larva
hatches from the egg and swims to
another host fish where it attaches by
its opisthaptor and develops into an
adult.

5. Class Cestoidea (Gr. kestos, girdle + eidos,
form),
• Commonly called tapeworms or cestodes.
• 3,500 species.
• Endoparasites: Reside in the vertebrate digestive system.
• Range from 1 mm to 25 m in length.
• Two unique adaptations:
Lack a mouth and digestive tract, absorb nutrients directly across their body
wall.
Proglottids: long series of repeating units. Contains one or two complete sets of
reproductive structures.
• Two Subclasses:
• Subclass Cestodaria contains about 15 species of fish parasites.
• Subclass Eucestoda contains medically important tapeworms.

6. Subclass Eucestoda
• True tapeworms.
• No mouth is present.
• Three regions of body:
 Scolex: Holdfast structure containing circular or leaflike suckers, anchors tapeworm to
the intestinal wall of its definitive vertebrate host.
 Neck: Posterior to the scolex, Transverse constrictions in the neck give rise to the third
body region, the strobila.
 Strobila: A series of linearly arranged proglottids, which function primarily as
reproductive units.
Types of Proglottids:
• Anterior proglottids: Immature
• Midregion proglottids: Mature
• Posterior proglottids: Accumulated eggs are gravid (L., gravida, heavy, loaded, pregnant)

8. Cont.…
• Monoecious.
• Each proglottid contains one or two complete sets of male and female reproductive
organs.
• Testes: Scattered throughout the proglottid
• Cirrus: Duct system deliver sperm
• Genital pore: Shared opening of male and female system.
• The male system of a proglottid matures before the female system,
• Copulation: Occurs with another mature proglottid of the same tapeworm or with another
tapeworm in the same host.
• Ovaries: Single pair in each proglottid, produces eggs.
• Sperm stored in a seminal receptacle fertilize eggs as the eggs move through the oviduct.
• As eggs accumulate, the reproductive organs degenerate; thus, gravid proglottids can be
thought of as “bags of eggs.”
• Eggs are released when gravid proglottids break free from the end of the tapeworm and
pass from the host with the host’s feces.

10. Some Important Tapeworm Parasites of
Humans
Taeniarhynchus saginatus: beef tapeworm
• Adults live in the small intestine.
• may reach lengths of 25 m.
• 80,000 eggs per proglottid.
• Oncosphere: a six-hooked (hexacanth) larva.
• Intermediate host: Cattle
• Digestive enzymes of the cattle free the oncospheres, and the
• Larvae use their hooks to bore through the intestinal wall into the bloodstream.
• Cysticercus (pl., cysticerci) or bladder worm: The bloodstream carries the larvae
to skeletal muscles, where they encyst and form a fluid-filled cysticerci.
• Definitive host: When a human eats infected meat (termed “measly beef”) that is
raw or improperly cooked, the cysticercus is released from the meat, the scolex
attaches to the human intestinal wall, and the tapeworm matures.

12. Some Important Tapeworm Parasites of
Humans
Taenia solium: pork tapeworm
• life cycle similar to that of Taeniarhynchus saginatus, except that the
intermediate host is the pig.
• 10 m long, but 2 to 3 m is more common.
• Cause cysticercosis and can be fatal if the cysticerci encyst in the
brain.

13. Some Important Tapeworm Parasites of
Humans
Diphyllobothrium latum: broad fish tapeworm
• Bothria; sing., bothrium: Scolex with two longitudinal grooves, act as holdfast structures
.
• Adult worm length 10 m.
• Shed up to a million eggs a day.
• Release eggs through uterine pores.
• Coracidia (sing., coracidium): ciliated larvae by hatching of eggs in freshwater.
• Intermediate host: small crustaceans and fish
• These coracidia swim about until small crustaceans called copepods ingest them.
• Procercoid larvae: coracidia developed in non ciliated larva in crustaceans.
• Plerocercoid larvae: When fish eat the copepods, the procercoids burrow into the
muscle of the fish.
• Larger fishes that eat smaller fishes become similarly infected with plerocercoids.
• Definitive host: humans (or other carnivores) when eat infected, raw, or poorly cooked
fishes, the plerocercoids attach to the small intestine and grow into adult worms.