PLATYHELMINTHES Flashcards
Superphylum Bilateria encompasses all animals with what key characteristic? What lineage are Platyhelminthes?
Origin of a 3rd cell layer/ bilateral symmetry
Platyzoa
Key characteristics
- unsegmented or free living worms
- dorso ventrally flattened
- combine sexual and asexual stages
- bilaterally symmetrical
- gut blind ending or absent
- majority are hermaphrodites
What has changed since Cnidaria? (4 things)
- triploblastic (mesoderm, endoderm, ectoderm)
- longitudinal nerve cells and first brain termed ‘cerebral ganglion’
- some terrestrial forms
- protonephridia involved in osmoregulation
Parasites within Platyhelminthes ?
Whats the other class ?
Phylum similar in form to free living flatworms ? What do they lack ?
1 ) Trematodes ( flukes with intermediate hosts )
Cestodes ( tapeworms )
Monogenea ( flukes , 1 host )
2) Turbelleria (free living worms) containing Polycladida and Tricladida
3) Acoela, a gut
New tissues
1) muscles
gonads (gamete producing)
excretory system
Why are flatworms so flat?
Lack of gas transport system limits dimensions
1) Why is there a need for serial repetition?
2) what is serially repeated?
1) Addition of mesoderm results in deeper tissue that needs nutrient supply and waste removal
2) In Platyhelminthes, transport is achieved by repetition of digestive and excretory systems down the body
• Other organ systems are also repeated either to control (nerve ganglia) or utilise (gonads) the resources
provided
1) Properties of Platyhelminth ciliated and permeable skin
2) Consequences
1) permeable for gas exchange
ciliated for locomotion
parasites show modification to resist attack or for attachment
2) Water loss or inflow
Function of protonephridia in dealing with water inflow
and waste removal
Contain flame cells and ladder-like network of excretory
ducts to stop water inflow
Bilateral symmetry allows ____ _____. Concentration of what sense organs. Where does light enter ? How is it processed?
head development
- Cup ocelli concentrated in cerebral eyespot
- Where there is no pigment
- A somewhat brain, high concentration of ganglion
Free living forms are usually _____. Can also reproduce by?
Larval stages are ciliated ___ larvae ?
hermaphroditic
fission and regeneration
Muller’s larvae
Parasitic innovations
Why have complex lifecycles?
1) - high egg output
- asexual reproduction by immature forms in intermediate hosts
2) Using intermediate hosts that are easy to find
• Moving up food chains
• Using vectors
The class Turbelleria is split into 2 orders: polycladida, meaning a multibranched (a) and (b) meaning 3-branched gut.
a) gut
b) tricladida
Why would parasites produce so many eggs?
- cannot survive outside of host unless as eggs
- sensory systems can only locate hosts at short range
- high larval failure
- costs of reproduction less crucial
Definitive host is where the parasite (a) reproduces and intermediate hosts are occupied by (b) which can reproduce (c).
a) sexually
b) larvae
c) asexually
