Platyhelminthes Flashcards
How many germ layers do the platyhelminthes have?
3
Ectoderm, endoderm, mesoderm
What do the 3 germ layers develop into?
Ectoderm - outer covering and the nervous system
Endoderm - gut and associated structures
Mesoderm - muscles, body cavity (coelom), circulatory system, most internal support structures
What are the three different ways a coelom can be represented in invertebrates?
Acoelomate - lacks body cavity between the gut and the outer body
Pseudocoelomate - body cavity is only partially lined by mesoderm
Coelomate - body cavity is completely lined by mesoderm (contains 2 layers of mesoderm therefore is a true coelom)
Are platyhelminthes protostomes or deuterostomes? Give some factors of the one they belong to.
Protostomes
Have spiral and determinate cleavage
Has schizocoelous coelom formation (mesoderm splits to eventually form the coelom)
Mouth develops from the blastopore
Are Xenacoelomorpha platyhelminthes?
Originally thought to be platyhelminthes but are more simplistic than that - part of their own phyla
Give the main features of Platyhelminthes
Triploblastic
Acoelomates
Bilaterally symmetrical
Undergone cephalisation
Have organs (due to 3 body layers)
Dorso-ventrally flattened
75% are parasitic
Free-living forms are found in aquatic or damp environments
How many gut openings do platyhelminthes have?
One
Give basic overview of the platyhelminthes nutrient uptake
Draw in fluid from surrounding areas
Absorb what is needed
Secrete the rest as waste
Do platyhelminthes have circulatory or respiratory systems?
No - this causes size constraints
How do some Platyhelminthes undergo locomotion?
Some have cilia on the bottom
Larger platyleminthes use muscular contraction instead
What does phototactic negative mean? Why do platyhelminthes have this?
Avoids light
Prone to dessication so would dry out in the light
What are neoblasts?
Totipotent cells that when activated can reform lost tissue aka regeneration
What were the Thompson and McConnell expierments on Platyhelminthes?
Paired a bright light with an electric shock
Learnt to associate the light with a shock
Then chopped the animals in half and they still responded
Mashed up the trained worms and fed them to non-trained worms and the non-trained worms showed a response (possibly due to observor bias - results never been reproduced)
McConnell suggested memory transfer is chemical
What are more recent experiments done on Platyhelminthes? What do they show?
Recent experients have trained the Platyhelminthes to tolerate light and space - two things they hate
Chopped off the heads of the trained worms and when they regenerated they still tolerated light and space
Show memories are possibly not stored in the head. The training possibly causes chemical changes in the animal - back of McConnell theory??
What type of reproduction do flatworms undergo? How is this done?
Sexual reproduction
Mutual exchange of sperm
However, some only want to give sperm and no receive and this causes penis fencing
What adaptations do parasitic platyhelminthes have?
Loss of unwanted organs e.g. the gut
Penetration devices
Attachment devices - to remain its position in the host
Protective devices - prevent host digestive enzymes from working on them
Transmission via a vector
Production of eggs e.g. in large numbers
What adaptations do Flukes (trematodes) have?
Tegument (which is non-cilliated syncytium)
Tegument is for protection, diffusion and nutrient uptake
Do not have a gut
Have oral and ventral suckers which contain enzymes to start digestion
Most are hermaphrodites
Give the generalised life cycle of a fluke
Definitive host contains adults parasite
Eggs are released (usually by faeces) into the water
Eggs hatch into larvae (miradicium)
These are uptaken into the first intermediate host e.g. a snail
Develop in the intermediate host to form a sporocyst
Sporocyst develops into a redia
Redia develops into a cercaria
This is then excreted and taken into a second intermediate host e.g. a fish
Forms a metacercaria and then develops into the adult stage
Released from the second intermediate host and enters the defintive host to repeat the cycle
What does Diplostomum spathaceum cause in the intermediate host? Why?
Causes cataracts (in fish)
Blinds the fish so it makes it easier for a gull (the defintive host) to catch and eat it and the parasite
Give the life cycle of a lancet fluke
Parasite lives in the bile duct of cattle/sheep
Produces a miracidia that is excreted and taken up by a snail
Snail secretes parasite in slime balls and these are uptaken by ants
The parasite forms cycsts in the ants
The parasite causes manipulated behaviour in the ants:
- ants leave the colony and climb to the top of some grass
- the ant clamps mandibles to the grass and stays there
- when the temp increases, they unclamp and join the colony
This repeats until the ant is eventuallt eaten by a sheep/cow (the defintive hosts) and the cycle repeats
What are co-operative trematodes?
Colonies of trematodes form within the mollusc host
This causes the division of labour e.g. some for reproduction, some are soliders
The soldiers are more active and either defend or attack other colonies that are either same or different species
What are the adaptations of tapeworms (cestoidea)?
Surrounded by tegument - protective layer
No gut
Scolex - concentrated nervous system is here and embeds in the intestines of the host via a sucker
Strobila - each section is a proglottids and is formed in the neck region
Have intermediate host(s)
