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
Briefly describe the lifecycle of Diplostomum spathaceum (eye fluke)
- Snail first intermediate host
- Fish second intermediate host
- Bird final host
- Parasite causes fish to develop cataracts → relies on it being eaten by bird
- When parasite at most infective stage inside fish, cataracts are worst
Describe the lancet fluke & its lifecycle
- Lives in bile duct of ruminants e.g sheeps, cows
1. Eggs passed in faeces / urine - Miracidian larvae
2. Eaten by snail, develop within
3. Release cercariae larvae in slime balls, ants attracted to slime balls
4. Take slime balls back to nest and feed on them
5. Metacercariae form inside ant → brain → changing ant behaviour
6. Ants climb to top of grass (at dawn and dusk time, when remnants feed)
Describe the tapeworms (cestoidea)
- Tegument
- No gut
- Scolex → head region made up of hooks and suckers
- Strobila → madeup of proglottids, packed with repro tissue
- Definitive host - Human
- Intermediate host - cow
- Mutual copulation
= Self fertilisation when only one worm
