Platyhelminthes (flatworms) Flashcards
(36 cards)
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
