PLatyhelminthes

Question 1

What are playhelminthes?

Answer 1

Flatworms.

Question 2

Where are they found?

Answer 2

Terrestrially, freshwater, marine waters and ephemeral pools.

Question 3

Which group are they classified within?

Answer 3

The lophotrochozoa.

Question 4

List 5 synapomorphies of Platyhelminthes.

Answer 4

1. Dorsoventrally flattened
2. Mostly hermaphrodite (although can be dioecious)
3. Acoelomate
4. A blind gut (only a single opening, no anus)
5. Possess an integument

Question 5

Define an integument.

Answer 5

A tough, outer protective layer. Often ciliated in free-living species.

Question 6

Excretion is via the protonephridia. What are they?

Answer 6

Similar to kidneys: a network of dead-end tubules with no internal openings. Tubules end in flame cells.

Question 7

Platyhelminthes possess totipotent cells throughout their lifetime. True or false?

Answer 7

True: they have hugely regenerative properties.

Question 8

Define a flatworm neoblast.

Answer 8

A somatic stem cell, have huge nuclei.

Question 9

What is characteristic about cell division in Platyhelminthes?

Answer 9

Their stem cells are the only cells to divide. A stem cell will divide into a terminally differentiated cell and another stem cell. The stem cell will go onto divide and the other cell will not.

Question 10

There are 2 major groups of Platyhelminthes that vary in lifestyle. What are they?

Answer 10

1. Turbellarians

2. Neodermata

Question 11

What are the turbellarians?

Answer 11

Free-living, however many enter endosymbiosis with other animals.

Question 12

Why are turbellarians often used as regeneration models?

Answer 12

If you chop them into bits, as long as each part has at least one stem cells it can grow into a whole new organism.

Question 13

What are the neodermata?

Answer 13

Obligate parasites, most species fall into this category.

Question 14

Give some examples of neodermata.

Answer 14

Blood flukes, tapeworms, monogeneans.

Question 15

What were the ancestral hosts for neodermata?

Answer 15

Fish, both chondrichthyans and osteichthyhans. Now it is all vertebrate species.

Question 16

What are the 2 styles of parasitism?

Answer 16

1. Active: organism seeks out a host

2. Passive: organism is accidentally consumed

Question 17

How do many flatworms evade the immune system of their host?

Answer 17

By secreting toxins or enzymes from their tegument.

Question 18

Parasites are often referred to as R-strategists. What does this mean?

Answer 18

They have massive reproductive outputs with no parental care.

Question 19

How many eggs can organisms generate per day?

Answer 19

~10,000s, they have huge uteruses.

Question 20

What are the 3 main species of neoderm?

Answer 20

1. Trematoda: the flukes
2. Cestoda: the tapeworms
3. Monogenea: fish parasites

Question 21

What are the blood flukes called?

Answer 21

Digenea.

Question 22

Digenea is the most diverse flatworm group. How many species are there?

Answer 22

~18,000.

Question 23

Digenea need between 3-5 hosts. What is always the primary host?

Answer 23

A snail.

Question 24

Schistosoma mansoni is a human parasite. What is characteristic about reproduction in this species?

Answer 24

The female will not sexually mature until she is within proximity of a male. She then lives permanently in his gynaecophoric canal.

Question 25

What disease does schistosoma mansoni cause in humans?

Answer 25

Schistosomiasis.

Question 26

What disease does schistosoma mansoni cause in humans?

Answer 26

Schistosomiasis.

Question 27

Where does schistosoma mansoni live in humans?

Answer 27

In the blood vessels, although the eggs must be released into the gut for excretion to continue the lifecycle.

Question 28

In cestoda (tapeworms), what percentage of the body is made of reproductive segments?

Answer 28

95%: each segment contains both male and female organs.

Question 29

Cestodans have lost discrete skin cells. Their surface is effectively one giant cell. What advantage does this have?

Answer 29

Increases surface area for substance diffusion.

Question 30

Many cestodans have lost their digestive systems. Why?

Answer 30

They are mostly enteric (gut) parasites and absorb already digested nutrients through their surface.

Question 31

What is the primary host of a cestodan?

Answer 31

An arthropod.

Question 32

What kind of parasitism do tapeworms have, active or passive?

Answer 32

Passive.

Question 33

There are only ~4-5 species of cestodan that infect humans. When is infection most dangerous to us?

Answer 33

When we are the intermediate hosts.

Question 34

What is characteristic about monogeneans in contrast to digeneans/cestodans?

Answer 34

They are external parasites, whereas the other 2 are internal.

Question 35

Where do monogeneans attach to their fish hosts?

Answer 35

On the gills and skin.

Question 36

Diplozoon paradoxum is a monogenean with extreme phenotypic plasticity. How does it become an adult?

Answer 36

Hermaphrodite larvae fuse to form an adult - even the internal duct-work fuses within them.