Platyhelminthes Flashcards
General features of all Platyhelminthes
Triploblastic and acoelomate Bilaterally symmetrical Cephalisation - concentration of nervous tissue at anterior end Some organ development Dorsoventrally flattened No transport systems - rely on diffusion Gut has one opening
Protonephridia
Simple excretory system
the tube connects with the outside of the animals body
Flagella within the flame waft, drawing in fluid from the surroundings and into protonephridia
Absorbs useful substances and waste is passed out
Turbellarians - structure and traits
Free living form
Have longitudinal and circular muscle fibres
Covered in an epidermis and use cilia for movement, secretes a mucous
Can move by body undulations
In the gut, the mouth leads to the pharynx leading to a branched gut
Turbellarians - eating
Insert their pharynx into decomposing material
Release enzymes and make it into a broth
Suck this broth into gut
Take up the resulting little fragments into the gut
Intracellular digestion then occurs
Also engulfs things whole into their pharynx - not always decomposing material
Turbellarians - sensory structures
Nervous system - concentration at anterior end and trunk nerves run down the body
Have simple eyes - eye spots or pigment cup eyes for detecting light (like jellyfish)
Negatively phototactic
Oracles on side of head for detecting chemicals
Turbellarian regeneration
Can regenerate head if chopped up
The further down the body the cut, the longer the head takes to reform
From experiments - gets very confused if regenerating from a small bit of tissue - 2 heads
Some kind of gradient cells are responding too
Cells are pluripotent
Thompson and McConnell Turbellarian experiments
Paired bright light and electric shocks Cut worms up - regeneration New regenerated worms responded as previous Fed trained worms to new worms These reacted in the same way Chemical transfer of memory... Results not been repeated Recent studies show passing on so (like first part) - changes in DNA as learns?
Turbellarian reproduction
Are hermaphrodites
Some pair up and exchange sperm (both fertilise eggs)
Penis fencing - fighting they don’t have to be the female which is costly
Parasitic Platyhelminthes
Derived from the free-living forms
Loss of unwanted organs (gut and sensory) - can use host’s
Penetration devices - enzymes or burrow into hosts
Attachment devices (hooks or suckers) to attach in or outside
Protective coverings to prevent being digested chemically by enzymes
Change their form to prevent immune systems working
Can be transmitted by a vector - can develop there
Eggs produced in large numbers - boost numbers by asexual reproduction
Trematodes features
Surrounded in tegument - non-ciliated syncytium
-protects but different to epidermis
-allows various molecules through (selective)
Suckers - ventral and oral that leads to pharynx and gut
Found in animals guts mainly
Reproductive tissue makes most of body
Hermaphrodites - sperm exchange
Makes 10,000-100,000x more eggs than free-living
Generalised lifecycle of Trematoda
- egg hatch in water - into intermediate (often snail)
- burrows into host and forms sporocysts (germinal cells inside) - Followed by redia larval stage - asexual R
- Germinal cells help to form cercaria larvae
- Swim around and burrow into 2nd intermediate (if have one) and form a metacercaria
- needs to be eaten by definitive host - Taken up by final host develops into adult and reproduces
Blood flukes - schistomatidae
Causes schistosomiasis (widespread)
Has separate sexes - females live in groove of male
1. F attracted to M by chemicals and come together
2. Release eggs which burrow into beans - released in faeces or urine
3. Eggs released into water make way into snail
4. Sporocyst stage - divide here, no redia, germ cells form into cercaria stage
5. Cercaria released into water, burrows through skin of human
6. Migrates round body into veins where mature etc.
Will cause death.
Children with these not allergic to stuff…
Displostomum Spathaceum
Flukes first intermediate is snail, second fish, final seabird
Causes cataracts in rainbow trout, reducing its escape response, making more vulnerable to seabird predation
Makes most blind when fluke at its most infectious
Lancet Fluke
Final = sheep or cow
1. Lives in gut of final, eggs released in faeces
2. Taken up by snail - cercaria larvae formed
3. Released in balls of mucous
4. Taken up by ants which eat this
5. Changes their behaviour - move up grass when cool making vulnerable to be eaten by final host
- if not eaten and warms, climbs down and carries on
= maximises transmission
Co-operative trematodes
-All related (asexual R)
Get differentiation in these
-Soldier forms small and aggressive
-Reproductive forms - go on to next (cercaria) form
-All found in same host
-Will protect each other from things like other parasites or flukes
