L11 Trematodes

Question 1

How many hosts do worms of the Subclass Digenea have

Answer 1

Two

Question 2

What is sequential polyembryony

Answer 2

The production of multiple embryos from the same zygote with no intervening gamete production

Question 3

Give the three subclasses of trematodes

Answer 3

Subclass Digenea
Subclass Aspidogastea 
Subclass Didymozoidea

Question 4

Give the three subclasses of trematodes

Answer 4

Subclass Digenea
Subclass Aspidogastea 
Subclass Dizymozoidea

Question 5

Give the basic characteristics of the Subclass Digenea

Answer 5

Have at least two hosts 
Dorsoventrally flattened 
"Fluke shaped"
Have one ovary with two testes 
Have a muscular mouth and an acetabulum 
Strongly r selected species 
Have vitelline glands which produce the egg cell and yolk 
Have a looping uterus
Two blindly ending intestinal tracts (no anus)

Question 6

Describe the many body types of Digenea

Answer 6

Echinostome 
Schistosome 
Monostome 
Holostome 
Amphistome 
Distome

Question 7

List the lifecycle stages of the trematode and the parts of the host in which they dwell

Answer 7

Egg- the definitive host
Miracidium- intermediate host
Sporacyst- intermediate host
Rediae- the hepatopancreas of the intermediate host
Cecaria- intermediate host
Metacecaria- second intermediate host , can be found on vegetation (infective stage)
Adult- the definitive host

Question 8

Name the common intermediate host of trematodes

Answer 8

Mulluscs

Question 9

Explain the classifications of the digenea egg

Answer 9

Type A- underdeveloped when leaving the host (Eg. passed in stool), undergoes embryonation outside of the host
Type B- partially developed leaving the host, only a brief period outside of the host is needed for embryonation
Type C- fully developed when leaving the host Eg. Schistosoma

Question 10

Describe the structure and function of the parts of the miracidium

Answer 10

Apical papilla- Point of attachment to snail
Eye spot- Gives ability to sense light
Penetration glands- To penetrate the host
Ciliated plates- For locomotion
Germ cells- Produce the next larval stage

Question 11

Describe the structure and function of the parts of the sporocyst

Answer 11

Sac- like structure filled with germinal cells
No digestive system, instead food is digested via the tegument (body wall)
Post larvae released through a birth pore

Question 12

Explain the morphological processes which lead to the formation of a sporocyst from the miricidium

Answer 12

The internal portion becomes vacuolated
Loss of the ciliated epidermal cells
The microvillous tegument is exposed
Eye spots are lost

Question 13

Describe the structure and function of parts of the redia

Answer 13

Procrusculi- used to move around

Primitive gut- most nutrients absorbed via tegument

Question 14

This post larval stage is responsible for parasitic castration

Answer 14

The redia (singular, plural is rediae)

Question 15

Describe the parts and functions of the cercaria

Answer 15

Oral sucker 
Acetabulum 
Germinal cells- give rise to the gonads 
Intestine with intestinal ceca 
Cystogenic glands- produce a cyst around the organism to form metacecaria 
Tail- used for locomotion, possess

Question 16

What are the four body types of cecaria

Answer 16

Gymnocephalus- “Naked”
Trichocercus- “Hairy”
Furcocercous- “Forked”
Microcercous-“Two colored”

Question 17

Describe the parts and function of the metacecaria

Answer 17

Cyst wall- composed of tanned protein and fibrous tissue (thinner within secondary host versus an external environment)

Question 18

Explain the routes of infection with Digenia

Answer 18

1. Through digestion of metacecaria and excystation in the intestine followed by migration
2. By penetration followed by migration

Question 19

Give a situation in which contraction of a Digenian infection may occur through penetration of cecaria

Answer 19

Schistosoma in water bodies may be absorbed through the skin, they are attracted to the warmth of humans. These infections tend to not be associated with the intestine but other parts of the animal such as the blood

Question 20

List the biochemical triggers needed for excystation of the metacecaria

Answer 20

• Acidic conditions
• Digestive enzymes
• Bile salts
• An elevated temperature
  (Mammal -37 which is higher than the temperature of the environment)
  Low redox potentials (Like having CO2)

Question 21

What follows the ecystation of metacecaria in the definitive host?

Answer 21

Migration of the parasite, somatic growth and development of the gonads leading to the formation of gametes

Question 22

Describe the directional movement of cecaria

Answer 22

Tail first