Gastropoda

Question 1

4 main changes in gastropods

Answer 1

1. Development of head - presence of tentacles (1 or 2 pairs) and eyes = more sensory apparatus
2. Dorso-ventral elongation of body - grow upwards = coiling of visceral mass and shell
3. Shell moves from protective shield to protective retreat
4. Torsion - visceral mass and mantle cavity rotate 180 - so over head

Question 2

Process of torsion

Answer 2

It ties its nerve cord in a knot to rotate itself
Gills are on opposite sides to where they were
Occurs by combination of muscle contractions and differential growing

Question 3

Reasons for torsion

Answer 3

Occurs in veliger larva stage (after trochophore) - may allow larval stage to climb in cavity for protection (no clear evidence)
Protection of adult?
Utilisation of oncoming water by gills - clean (before was at back so not fresh)
Disadvantage is now anus is over head - not ideal

Question 4

Impacts of torsion

Answer 4

Sanitisation problem of torsion
-some have holes in shells to allow water in to ensure cleanliness (release soiled from anus)
-keyhole limpet draws water in over gills and leaves top where anus and hole is
Some undergo de-torsion, can tell as NS still twisted sligthly
Sea slugs lost shell (bright colours, toxic and harbour nematocysts)

Question 5

Spiralling

Answer 5

Need to spiral as body grows
Initially symmetrical - planospiral
Not adaptive as it makes it very difficult for snail to move - so tips to 1 side - conispiral
-heaviness on 1 side = animal squished on that side, so see some reduction of organs
Spiralling mainly on right side, but see some ‘lefties’

Question 6

Pulmonates

Answer 6

Sophisticated group of gastropods (land snails and slugs)
Have lost gills
Vascularised mantle cavity
Allows them to go on land and breathe - rich blood supply
Use mantle cavity like a lung
Evolved when oxygen was short in ponds etc. so had to have a different way to access oxygen/air
Are hermaphrodites - exchange sperm, the production of love darts during reproduction

Question 7

Partula

Answer 7

Ecological disaster
Was a species rich genus in South Pacific (studied for years looking at speciation etc.)
Had problem with African land snail (pest)
Tried getting rid of it using predatory snail (Rosy wolfsnail)
Predatory didn’t eat pest, and went for partula instead
Only 10 spp left (from ~70)