Platyhelminthes (flatworms) Flashcards
Body symmetry / layers / cleavage
- Bilateral
- 3 body layers (triploblastic)
- Spiral cleavage - protostome: mouth develops first
- within spiralia group on evolutionary tree
Body structure
Acoelomate (no body cavity/coelom
Dorso-ventrally flattened
High surface area to body ratio
some organ development
No circulatory system
Cephalization
concentration of nervous tissue at one end (anterior end)
Why must they be aquatic?
Susceptible to drying because they are so thin
what percentage of platyhelminthes parasitic?
75%
rest are free-living form
The gut of free-living forms
Gut has one opening
can be simple or complex
pharynx serves as anus and mouth
What are oracles? (body structure)
stick out of head and detect chemical signals
Waste excretory system name
Protonephridia
simple system
Waste excretory system mechanism
- Protonephridia
- Flame bulbs: branched guts that end in ‘bulbs’ with flagella on the end.
- Flagella waft materials and waste products through a tube system,
- Absorb anything that is useful and excrete anything that isn’t*
How are platyhelminths linked to Xenacoelomorpha?
Xenacoelomorpha are basal bilaterians once thought to be platyhelminths because of their similar body structure
separate sister group
Flatworm body movement
Longitudinal and circular muscles around the body
Cilia and gland cells - produce mucus - allow movement
Some ungulate body for movement
Nervous system
Nerve branches run down body from anterior to posterior
mechanisms of sight
Negatively phototactic (move away from light)
Form of protection (avoiding drying out)
Simple eyes -Detect light
Reproductive organs
Hermaphrodite
both male and female reproductive organs
Regeneration
Can reform parts of body
different size cuts create different regenerations
A smaller cut leads to two heads forming instead of head and tail.
further down the animal regeneration takes longer
Mechanism of regeneration
- Neoblasts (stem cells) activated to reform lost tissue
- Activated by some sort of chemical gradient
- A possible explanation of why lower down the body regeneration is slower (lower concentrations of neoblasts?)
Thompson and McConnell experiment - Can memory be transferred chemically?
Trained flatworms with electric shocks and bright light
Chopped up and found that new regeneration also responded to light
Same happened when trained flatworm was fed to other animal
Suggested memory was transferred chemically
Possibly some bias in the experiment
More recent experiments suggest that memory can be transferred or stored after regeneration.
Sexual reproduction of flatworms
Pair up and have mutual exchange of sperm
What is penis fencing?
Fertilised offspring need investment so some species fight so that one can get the sperm in before the other
Acting as a male is less costly than being a female
Parasitic adaptations (modification of body to adapt)
- Loss of unwanted organs
- Penetration devices - some way of getting into host
- Attachment devices - a way of hanging onto the host
- Protective device - to prevent themselves from being attacked by the host
- Transmission via a vector - complex life cycle
- Production of eggs in large numbers
Flukes (trematodes): Tegument
- Non- ciliated syncytium: Cells without any boundaries
- Protective coat
- Allows diffusion and some nutrient uptake
- Protects the parasite from host immune factors and serves as an absorptive surface for the acquisition of nutrients
Fluke pharynx
used to feed - strong sucker
Fluke reproduction
Most of the animal is dedicated to reproducing
produces 10,00 - 100,000 x more eggs than free living flatworm
hermaphrodite
Flukes: excretion / nervous system
Protonephridia - simple excretory system
simple nervous system
Generalised life cycle of a fluke
- Eggs released from difinitive host in faeces, urine and sputum (spit) - often into water
- Miracidium forms (ciliated larvae) swims around then encounter 1st intermediate host (often snail)
- reproduce and form Redia larvae then Cercaria larvae
- Cercaria are released and encounter 2nd intermediate host
- Form Metacercaria - then taken up by definitive host
- Cycle begins again
what do Blood Flukes cause?
schistosomiasis
causes necrosis of organs
Blood fluke sexes
have separate sexes
female lives in groove in males body
pair up for life
Blood fluke lifecycle
- Eggs released in faeces or urine into water
- Miracidium forms (ciliated larvae)
- Penetrate snail host
- Cercaria larvae released and burrow into skin using enzymes to break down skin and tail to burrow
- Make their way through the blood system into bladder or intestine (definitive host)
blood Fluke worm genome
lots of enzymes for breaking down proteins - can’t make own fats
bloodfluke infection - allergies?
people who have blood fluke infection have fewer allergies
Diplostomum spathaceum parasite (in fish)
- Parasite causes fish to form cataracts
- When the parasite is ready to be passed on the cataract is at its highest stage
- Fish with well-developed cataract are easier for birds to catch
- Birds are the definitive host
Lancet fluke
- Lives in bile duct of ruminants
- Miracidia larvae are passed to particular snail species
- Cercariae larva are released in slime balls
- Ants collect slime balls, take to nest and feed on them
- Cecariae from into metacercaria within ants
- Causing ants to change their behaviour
- Ants climb to the top of grass blades and clamp on to where ruminants would eat and wait to get eaten by the final host
- Does this daily until eaten
Co-operative trematodes
- Lots of different larvae from different species / different parents infect a host
- Division of labour
- Some are reproductive ones and others are solider
- Soldier larvae will attack other individuals that aren’t related or from a different species
Tapeworms (cestoidea)
- Tegument
- No gut
- Scolex - hooked head region that attaches to host intestine
- Strobila (proglottids, formed in neck region) - packed full of reproductive tissue
- Have Intermediate host(s)
What are platyhelminthes?
Flatworms
Larval staged within Flukes
- Miracidia
- Redia
- Cercaria
- Metacercaria
