1: Platyhelminthes Flashcards
Describe the Platyhelminthes
(Flatworms)
Protostomes → triploblastic (3 body layers)
- No body cavity (coelom) - mass of mesoderm
- Bilaterally symmetrical
- Cephalisation
- Organ development
- Dorso-ventrally flattened
- 75% parasitic
What is cephalisation?
Conc. of nervous tissue in anterior end
Platyhelminthes are dorso-ventrally flattened. What does this mean for its habitat?
They have high SA:V, but susceptible to drying out so they live in damp conditions
Describe the excterory system of the Platyhelminthes
Protonephridia:
- Branched system with flame bulbs (flagella)
- Wafts fluid down canals, useful reabsorbed/waste excreted
- Simple kidney
Describe the body features of the Platyhelminthes
- Gut has one opening
- Solid mass of mesoderm - no cavity
- No circulatory system
- Longitudinal and circular muscles
- In free living form → cilia and gland cells to produce mucus
Describe the sensory system of the Platyhelminthes
Nerve branches
Simple eyes → negatively phototactic (move away from light, to avoid desiccation)
Oracles → detect chemical queues
Can have nematocysts
Describe how Platyhelminthes can regenerate
Can chop into bits and it will regenerate. due to:
Neoblasts → activated to reform lost tissues
Cells respond to chemical gradient in animal
Describe Thompson & McConnel 1950s & 60s experiments on Platyhelminthes biochemical memory
Trained worms, paired bright light & electric shock
* After chopping them up, the reformed worm responded in the same way to the light
* Next step: fed a trained worm to an untrained worm = untrained worm had conditioned response!!
= Suggested memory was transmitted chemically → however results never reproduced
Descirb sexual reproduction in the Platyhelminthes
Hermaphrodites:
- Usually they pair up, mutual exchange of sperm
- But, some species of flatworms don’t want to do this (want to avoid receiving sperm and have fertilised offspring):
- Penis fencing → fight so one gets the sperm in before the other then flees
75% of Platyhelminthes are parasitic, what sort of adaptations might they need?
- Loss of unwanted organs e.g gut, sensory
- Penetration devices
- Attachment devices
- Protective devices
- Transmission via vector
- Production of eggs, etc. in large numbers
What are the Platyhelminthes known as?
Flatworms
Describe the body plan of trematodes (flukes)
- Tegument (Non-ciliated synctium = cells without cell walls)
- Suckers (oral and ventral)
- Simple NS, protonephridia
Describe the reprodutive system of the Flukes
- Repro system produces 10,000-100,000 times more eggs than free-living
- Hermaphrodite (usually) and mutual copulation
What is the function of the tegument in flukes?
- Protection from hosts digestive and immune system
- Allows diffusion
- Waste removal
- Nutrient uptake
Describe the blood flukes (Schistosomatidae) life cycle
→ cause schistosomiasis (affects blood vessels)
- This species has separate sexes, female sits in a grove inside the male
- Eggs released in faeces / urine (depending on where they were living)
- Form larvae in water and penetrate snail host → (no radial stage) cercaria larvae produced and released from snail
- Carried via blood to veins of intestine/bladder