Platyhelminthes - Exam Questions

Question 1

What are the three classes of Platyhelminthes, and which two are medically significant?

Answer 1

• Class Trematoda
• Class Cestoidea
• Class Turbellaria (NOT medically significant)

Question 2

In what types of organs are the digenetic trematodes found in definitive hosts?

Answer 2

• Small intestine
• Liver
• Lung
• Blood vessels

Question 3

How many intermediate hosts are used in most species, what is the first intermediate host always going to be, and what type of reproduction occurs inside it?

Answer 3

• # of intermediate hosts –> 1 or 2
• 1st intermediate host –> snail
  - Type of reproduction –> asexual

Question 4

With respect to intermediate hosts, what is unusual about the schistosomes?

Answer 4

Schistosomes do not have a 2nd intermediate host + no metacercaria stage

Question 5

What general features distinguish the class Cestoidea from the class Trematoda?

Answer 5

Cestotidea:
o Segmented body
o No digestive tract

Trematoda:
o Non segmented body
o Incomplete digestive tract

Question 6

Where are adult tapeworms always found in humans?

Answer 6

small intestine

Question 7

What are the main external and internal structural features of the platyhelminth body? What are parenchymal cells?

Answer 7

• Flattened dorso-ventrally (leaf-like shape)
• Acoelomates
  - Parenchymal cells –> packing tissue
  around organs

Question 8

What is the osmoregulatory system of platyhelminths, and how does it function?

Answer 8

• Flame cell system (protonephridia)  helps
  worms adapt from FW to SW + remove water
  - Interstitial fluid btw parenchymal cells
  - Interstitial fluid filters thru membrane
  where cells interdigitate

Question 9

What is the stage that hatches from the egg? What is unusual about its body surface, compared to the body surface of the adult worm? What is the function of this stage?

Answer 9

• Miracidium
  - Function –> penetrate snail
  - Has an apical papilla (for penetration)

Question 10

What two types of progeny can be produced by a mother sporocyst, and how do these two stages differ from each other? In a single species of trematode, are both types of progeny produced? What stage is produced by mother rediae?

Answer 10

• Daughter sporocysts –> produces cercariae
  - Only produced in schistosomes
• mother rediae –> produces many daughter
  rediae

Question 11

What is the final stage produced inside the snail? Upon leaving the snail, what does this stage next become, and how? Why are schistosomes again an exception here?

Answer 11

• Cercariae –> becomes metacercaria when it penetrates the 2nd intermediate host
  - Schistosomes don’t have a 2nd
  intermediate host