Gastropods

Question 1

8 mollusc clades

Answer 1

1. Caudofoveata\ Aplacophora
2. Solenogastres
3. Monoplacophora
4. Scaphopoda: tusk shells
5. Polyplacophora: chitons
6. Gastropoda: snails, limpets, slugs etc.
7. Bivalvia: clams, mussels, etc
8. Cephlapoda: octopi, squid

Question 2

Characteristics of the Phylum Mollusca

Answer 2

One of the largest phyla - ~93,000 species (35,000 fossils)
Microscopic to ~18m (454kg)
Marine, fresh water and terrestrial
Grazers, carnivores, filter feeders
Most Gonochoristic, some hermaphrodites
All soft bodied (no skeleton), most secrete a hard shell
Coelomates

Question 3

Three main parts

Answer 3

Muscular foot: involved in movement, contains sensory organs
Visceral mass: digestive, circulatory, respiratory, reproductive and sensory organs
Mantle: fold of tissue draped over visceral mass. Excretes the shell (where present)

Question 4

Development

Answer 4

Most marine & aquatic molluscs have planktonic trochophore and veliger larval stages

Question 5

Snails, slugs, limpets, whelks, conch, sea hares, periwinkles, sea slugs, sea butterflies

Answer 5

75% all mollusc species
Only molluscs to have invaded land
Univalve coiled shell typical
Variously coiled

Question 6

Functional beauty of shells

Answer 6

The outer layer consists of conchiolin (tough protein)
The inner layers consist of calcium carbonate
The colours result from pigment in the calcareous layers

Question 7

Circulationin of snails, slugs, limpets etc

Answer 7

Heat delivers blood (haemolymph) to head/foot and viscera in mantle cavity
Open circulation
Blood also has role in hydrostatic skeleton

Question 8

Excretion (snails, slugs, limpets etc)

Answer 8

Only one nephridium (kidney) retained in gastropods
Waste from heart ultra-filtered into pericardial cavity
Drains into nephridium/kidney

Question 9

Feeding (Snails, slugs, limpets etc)

Answer 9

Highly varied
Most herbivorous (grazers/browsers)
Ciliary feeders (slipper limpets)
Scavengers
Predators (Mollusca, invertebrates & vertebrates)
Mostly use radula which may be extremely modified
E.g. venomous Conus spp.

Question 10

Gastropoda divided into 3 informal subclasses

Answer 10

Prosobranchia, Opisthobranchia, Pulmonata

Question 11

Prosobranchia

Answer 11

Periwinkles, limpets, whelk, conch, abalone, slipper shells, oyster borers, rock shells, cowries

Question 12

Opisthobranchia

Answer 12

Sea hares (vestigal shell), sea slugs, nudibranchs (cerata), canoe shells

Question 13

Pulmonata

Answer 13

Land and freshwater snails and slugs, lack gills, mantle cavity acts as lung.

Question 14

Nudibranchs

Answer 14

Nudibranchs have lost shells and brightly coloued
Dorid nudibranchs – make or accumulate toxins from food (sponges) secrete in mucus
Aeolid nudibranchs – graze on Cnidaria- have chitin coated gut & accumulate nematocysts in tips of protusions
APOSEMATISM- warning colouration

Question 15

Pulmonata Reproduction

Answer 15

Penises are everted
Sperm exchange is external
1. The shelled Helicidea the vagina contains an oval dart sac
2. The sac secretes a calcareous spicule- the ‘love dart’
3. Dart secretes hormones that increase sperm survival & paternity
4. Copulating limacid slugs hang from a cord of mucus attached to a tree
5. The penes are 10 – 25cm long