PLatyhelminthes Flashcards
What are playhelminthes?
Flatworms.
Where are they found?
Terrestrially, freshwater, marine waters and ephemeral pools.
Which group are they classified within?
The lophotrochozoa.
List 5 synapomorphies of Platyhelminthes.
- Dorsoventrally flattened
- Mostly hermaphrodite (although can be dioecious)
- Acoelomate
- A blind gut (only a single opening, no anus)
- Possess an integument
Define an integument.
A tough, outer protective layer. Often ciliated in free-living species.
Excretion is via the protonephridia. What are they?
Similar to kidneys: a network of dead-end tubules with no internal openings. Tubules end in flame cells.
Platyhelminthes possess totipotent cells throughout their lifetime. True or false?
True: they have hugely regenerative properties.
Define a flatworm neoblast.
A somatic stem cell, have huge nuclei.
What is characteristic about cell division in Platyhelminthes?
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.
There are 2 major groups of Platyhelminthes that vary in lifestyle. What are they?
- Turbellarians
2. Neodermata
What are the turbellarians?
Free-living, however many enter endosymbiosis with other animals.
Why are turbellarians often used as regeneration models?
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.
What are the neodermata?
Obligate parasites, most species fall into this category.
Give some examples of neodermata.
Blood flukes, tapeworms, monogeneans.
What were the ancestral hosts for neodermata?
Fish, both chondrichthyans and osteichthyhans. Now it is all vertebrate species.
What are the 2 styles of parasitism?
- Active: organism seeks out a host
2. Passive: organism is accidentally consumed
How do many flatworms evade the immune system of their host?
By secreting toxins or enzymes from their tegument.
Parasites are often referred to as R-strategists. What does this mean?
They have massive reproductive outputs with no parental care.
How many eggs can organisms generate per day?
~10,000s, they have huge uteruses.
What are the 3 main species of neoderm?
- Trematoda: the flukes
- Cestoda: the tapeworms
- Monogenea: fish parasites
What are the blood flukes called?
Digenea.
Digenea is the most diverse flatworm group. How many species are there?
~18,000.
Digenea need between 3-5 hosts. What is always the primary host?
A snail.
Schistosoma mansoni is a human parasite. What is characteristic about reproduction in this species?
The female will not sexually mature until she is within proximity of a male. She then lives permanently in his gynaecophoric canal.
What disease does schistosoma mansoni cause in humans?
Schistosomiasis.
What disease does schistosoma mansoni cause in humans?
Schistosomiasis.
Where does schistosoma mansoni live in humans?
In the blood vessels, although the eggs must be released into the gut for excretion to continue the lifecycle.
In cestoda (tapeworms), what percentage of the body is made of reproductive segments?
95%: each segment contains both male and female organs.
Cestodans have lost discrete skin cells. Their surface is effectively one giant cell. What advantage does this have?
Increases surface area for substance diffusion.
Many cestodans have lost their digestive systems. Why?
They are mostly enteric (gut) parasites and absorb already digested nutrients through their surface.
What is the primary host of a cestodan?
An arthropod.
What kind of parasitism do tapeworms have, active or passive?
Passive.
There are only ~4-5 species of cestodan that infect humans. When is infection most dangerous to us?
When we are the intermediate hosts.
What is characteristic about monogeneans in contrast to digeneans/cestodans?
They are external parasites, whereas the other 2 are internal.
Where do monogeneans attach to their fish hosts?
On the gills and skin.
Diplozoon paradoxum is a monogenean with extreme phenotypic plasticity. How does it become an adult?
Hermaphrodite larvae fuse to form an adult - even the internal duct-work fuses within them.
