Cestodes Intro

Question 1

What are some defining features of cestodes?

Answer 1

obligate parasites, entirely endoparasitic, no mouth or digestive tract, each proglottid has male and female sex organs (hemaphroditic)

Question 2

What are some features of the cestode life cycle?

Answer 2

no asexual phases, at least one intermediate host is required

Question 3

What types of animals are usually definitive hosts?

Answer 3

hunters

Question 4

What types of animals are usually intermediate hosts?

Answer 4

the prey of hunters

can be a mammal, an arthropod, a fish, a bird, a reptile

Question 5

What are the three distinct parts of a cestode body?

Answer 5

scolex, neck, strobila

Question 6

What is the difference in the scolex of the order Pseudophyllidea and Cyclophillidea?

Answer 6

Pseudophyllidea: scolex has slit-like suckers/grooves
Cyclophillidea: scolex contains suckers and sometimes hooks

Question 7

How can most tapeworms be distinguished?

Answer 7

by looking at the scolex

Question 8

What are some features of the neck?

Answer 8

undifferentiated and unsegmented, the narrowest part of the body, where new proglottids differentiate

Question 9

Define strobilization?

Answer 9

the synthesis of new proglottid segments from the neck so that the strobila becomes longer.
proglottids at the posterior end become more sexually mature

Question 10

What are the three types of proglottids?

Answer 10

immature proglottid (newly synthesized)
mature proglottid (have male and female sex organs)
gravid proglottids (develop after mating. have hundreds of embryonated eggs)

Question 11

What happens to gravid proglottids in the host?

Answer 11

male and female organs disintegrate as they are replaced with eggs, gravid proglottids detach from the strobila, and are either released in the feces intact or disintegrated to release the eggs

Question 12

What are the male sex organs?

Answer 12

many testes, vasa differentia, vas deferens (often highly coiled), cirrus sac with cirrus, common genital pore

Question 13

What are the female sex organs?

Answer 13

two ovaries, vitellaria (yolk gland), mehlis’ gland, uterus, vagina, common genital pore

Question 14

How do cestodes fertilize their proglottids?

Answer 14

self-mating within a segment is rare
sperm usually transferred to adjacent mature proglottids
each gravid proglottid can contain 100-1000’s of eggs

Question 15

What are some common characteristics of cestode eggs?

Answer 15

• passed eggs are always embryonated
• contain an oncosphere, which is encased in an inner evelope, which is surrounded by an embryophore. The outer envelope surrounds this and is covered by the shell/capsule
• can remain in external environment for weeks to months

Question 16

What is particular about the tegument of cestodes?

Answer 16

because they have no digestive tract, tegument also absorbs nutrients and must resists digestive enzymes of the host.
This is accomplished by the glycocalyx (carbohydrate-based) layer. there are many villi to increase surface area also

Question 17

What is the syntegument?

Answer 17

outer anucleate syncytial cytoplasmic layer containing mitochondria and secretory bodies

Question 18

What is the cytotegument?

Answer 18

nucleated cell bodies lying beneath the tegumental muscles and attached to the syntegument

Question 19

How do cestodes digest their food?

Answer 19

they do not secrete digestive enzymes. they rely on their host to do this for them. their tegument has evolved to competitively absorb host nutrients such as amino acids, sugars, fatty acids, purines, pyrimidines and vitamins

Question 20

How do cestodes respond to various osmotic pressures?

Answer 20

they have no control over their body volume: they swell in dilute solutions and shrink in concentrated solutions.
they appear to be slightly hypotonic to their surroundings

Question 21

Describe the cestode nervous system

Answer 21

paired ganglia in scolex, with nerves running down the body and forming a ladder-like shape.
the scolex features are richly innervated