Lophotrochozoa III: Molluscs Flashcards
1
Q
Describe molluscs
A
- hypothesised to be the second biggest phylum
- 100,000 species
- evolutionarily flexible body plan
- through-gut
- not segmented
- shell and mantle
- gills
- radula
2
Q
What is a shell?
A
- secreted by mantle tissue
- extracellular calcium carbonate + proteins
- conchin protein precipitates the CaCO3
- direction of the crystals dictates properties
- not moulted
- can only grow at edges
3
Q
Describe the structure of the cell
A
- surface protein (periostracum)
- chalky prismatic layer
- pearly, nacre layer
- mantle cells
- different calcium carbonate crystal structures in upper and lower layer
4
Q
What is a radula?
A
- specialised feeding structure
- ribbon with teeth, pulled tight over the cartilaginous odontophore (solid block)
5
Q
Give an example of a mollusc
A
- Lottia persona (limpet)
- also barnacles
6
Q
List the 3 major Classes of the Mollusca
A
- Gastropoda
- Bivalvia
- Cephalopoda
7
Q
Describe the Aplacophora
A
- 2 minor Molluscan Classes: Chaetodermomorpha and Neomeniomorpha
- rare
- worm-like
- no shell
8
Q
Describe the Monoplacophora
A
- fossils known with a single shell
- series of ‘muscle scars’ suggested ‘almost’ segmented body
- found in 500m deep Pacific Ocean trench
- e.g. Triblidyum reculatum
9
Q
Polyplacophora
A
chitons
10
Q
Scaphopoda
A
tusk shells
11
Q
Describe the Gastropoda
A
- one shell (sometimes lost)
- use radula to scrape algae of rocks, or eat lettuce
- generally slow-moving grazers
- torsion
12
Q
Describe torsion
A
- in development, body twists 180° anticlockwise
- hypothesised to have evolved as an advantage in hiding the head
13
Q
What are the evolutionary contraint of torsion?
A
waste products released over head and sense organs
14
Q
Describe the secondary adaptations to torsion
A
- hole in shell
- lose the right gill for sideways flow of water
- detorsion
15
Q
Describe the Land slug
A
- lost the shell
- low Ca++
- slime defence
