Cestoda Overview and Classification

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Questions and Answers

What is typically associated with the life cycle pattern of terrestrial parasites?

Multiple intermediate hosts

No intermediate host

Single intermediate host (correct)

Aquatic environments

What happens after the disintegration of the proglottids in the digestive tract of the host?

The eggs develop into adult worms

The eggs are released into the water

The oncosphere transforms into a cysticercus (correct)

The proglottids are expelled from the body

Where are the cysticerci typically deposited in the intermediate host?

In the muscular parts of the body (correct)

In the gastrointestinal tract

In the respiratory system

In the nervous system

Which of the following larval body plans is characteristic of terrestrial parasites?

Two larval body plans Signup and view all the answers

What is the role of the scolex in the life cycle of a terrestrial parasite?

It allows the parasite to attach to the host's intestine Signup and view all the answers

What is a primary feature of Cestoda that differentiates them from other helminths?

Have a body covered by an absorptive tegument Signup and view all the answers

In what way do cestodes reproduce?

They can self-fertilize due to their monoecious nature Signup and view all the answers

Which type of life cycle characteristic is associated with Cestoda?

Indirect life cycle with 1 to 2 intermediate hosts Signup and view all the answers

What is the term used for the unique segments of a cestode that contain reproductive tissues?

Proglottids Signup and view all the answers

Which of the following describes the scolex of cestodes?

The attachment structure with hooks and suckers Signup and view all the answers

Which statement best describes the reproductive strategy of Moniezia expansa?

Each proglottid contains duplicate sets of both male and female organs Signup and view all the answers

What type of organisms serve as hosts for the larval stages of cestodes?

Fish, amphibians, reptiles, birds, and mammals Signup and view all the answers

What characteristic is NOT associated with the strobili of cestodes?

Segmented body plan important for nutrient absorption Signup and view all the answers

What is protogyny in relation to reproductive organs?

Female organs mature before male organs. Signup and view all the answers

What role does the cirrus play in the reproductive process?

It is a protrusible copulatory organ that transfers sperm. Signup and view all the answers

Where are the oocytes fertilized in cestodes?

Inside the ootype. Signup and view all the answers

What happens to fertilized eggs after they are formed in the ootype?

They are released and pushed to the uterus. Signup and view all the answers

What describes the release of terminal gravid proglottids?

They can be released in groups or singly. Signup and view all the answers

Which term describes the excretion of empty proglottids mixed with feces?

Pseudo-apolytic Signup and view all the answers

What is a characteristic of the eggs formed by cestodes?

They can have operculum and can be thick-walled. Signup and view all the answers

What is the main function of the operculum in thick-walled, selectorized eggs?

To protect the embryo inside Signup and view all the answers

Which larval stage is characterized by a transformation into a procercoid?

Coracidium Signup and view all the answers

What phenomenon occurs when proglottids are found in the intestine after fertilization?

Euapolytic Signup and view all the answers

What organisms primarily serve as the first intermediate host for many aquatic tapeworms?

Zooplankton microcrustaceans Signup and view all the answers

In the life cycle of terrestrial parasites, what occurs in the hemocoele of the insect?

Transformation to cysticercoid Signup and view all the answers

What is the term for the six-hooked embryos found within eggs?

Oncospheres Signup and view all the answers

What type of hosts do aquatic tapeworms typically target for the completion of their life cycle?

Birds and amphibians Signup and view all the answers

Which of the following describes the condition the procercoid transforms into within its definitive host?

Adult tapeworm Signup and view all the answers

Which is NOT true regarding the life cycle stages of aquatic parasites?

Intermediate hosts are always terrestrial Signup and view all the answers

Study Notes

Cestoda

Belong to the Phylum Platyhelminthes
Parasitize fish, amphibians, reptiles, birds, and mammals
Hermaphrodite
Dorsoventrally flattened
Have an indirect life cycle with 1 to 2 intermediate hosts
Long patent period
Lack a digestive system
Body covered by an absorptive tegument
Larval stages in intermediate hosts are called metacestodes

Two Main Groups

Cestodaria:
- Not a significant group
- Have 10 hooks (decacanth)
Eucestoda:
- Have only 6 hooks (hexacanth)

General Features

Most cestodes consist of a scolex, neck, and strobila
The entire worm behind the scolex is called the strobila
Unique reproductive segments are called proglottids
Proglottids are continuous with tissues throughout the body
New proglottids form in the neck and move posteriorly

Scolex

The scolex is the anterior end of the worm responsible for attachment
Scolex morphology varies between species
Scolex is typically equipped with hooks and suckers

Reproduction

Most cestodes are monoecious
Each proglottid contains one set of male and one set of female organs
Self-fertilization is usually avoided due to protandry or protogyny
Sperm transfer occurs between proglottids of the same or different strobila

Reproductive Organs

Male:
- Testis
- Vas Deferens
- Seminal Receptacle/Vesicle
- Cirrus
Female:
- Ovary
- Yolk Stock
- Ootype
- Mehlis' Gland
- Uterus
- Vagina

Egg Formation

Oocytes are released from the ovary
Oocytes are fertilized within the ootype
Yolk cells are added to the zygote
Fertilized eggs are released from the ootype into the uterus
Gravid proglottids detach from the strobil and are expelled
Different species release eggs in various ways:
- Apolytic: Proglottids break off before releasing eggs
- Pseudo-apolytic: Eggs are released in the gut, and proglottids are empty when expelled
- Eupolytic or Hyperapolytic: Proglottids detach in the gut after fertilization

General Life Cycle

Aquatic Tapeworms:
- Eggs release an oncosphere or hexacanth
- Eggs or oncosphere are ingested by microcrustaceans or fish
- Oncosphere develops into a procercoid
- Procercoid transforms into a plerocercoid in the second intermediate host (fish)
Terrestrial Tapeworms:
- Eggs are ingested by invertebrates like insects
- Eggs transform into a cysticercoid
- Cysticercoid awaits ingestion by the definitive host

Metacestodes

Cysticercoid:
- Found in invertebrates
- Contains an invaginated scolex
Cysticercus:
- Found in vertebrates
- Contains an invaginated scolex with a bladder
Plerocercoid:
- Found in fish
- elongated and contains a cercomer tail

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Description

This quiz covers the general features, classifications, and life cycles of Cestoda, a group of parasitic flatworms. Explore the differences between the two main groups, Cestodaria and Eucestoda, and understand their unique characteristics. Test your knowledge about their anatomy and biology.