MolluscsMolluscs

Zoe Wong6s27

Classification:Classification:Phylum: MolluscaThe Phylum Mollusca contains the

following subgroups: Class: Aplacophora (solenogasters, deep-sea

wormlike creatures)Class: Bivalvia (clams, oysters, scallops,

mussels)Class: Cephalopoda (squid, nautilus, cuttlefish)Class: Gastropoda (snails, slugs, limpets, sea

hares)Class: Monoplacophora (deep-sea limpet-like

creatures)Class: Polyplacophora (chitons)Class: Scaphopoda (tusk shells)

Class ExampleGastropod chiton

limpetperiwinklesnail

Bivalve musseloyster

Cephalopod squidoctopuse

DiversityDiversityvary from 50,000 to a maximum of

120,000 speciesin 2001 estimated about 93,000 named

speciesHas been estimated that there are about

200,000 living species in total70,000 fossil species80% of all known mollusc species are

gastropods

CharacteristicsCharacteristics Soft-bodied animals Distributes in terrestrial and aquatic habitats An anterior head A ventral foot A dorsal visceral mass Surrounded by a thin fleshy mantle Sheltered in calcareous shell Exoskeleton Carry out respiration by gills Filter feeder

Body StructureBody Structure1 radula 2 mouth

3 shell 4 stomach

5 gonad 6 heart

7 coelom 8 nephridium

9 mantle 10 mantle cavity

11 anus 12 gill

13 foot 14 hemecoel

15 pedal nerve cord 16 gut

17 visceral nerve cord

18 nerve ring

ReproductionReproductioncan be sexualhave both male and female reproductive

organsmating happens during some particular time

and temperaturesnail stabs the skin of the other snail Female snail will then produce eggs internally

and then fertilized by the sperm that has been exchanged

around 1 month for the snail to lay eggs14 days to hatch2 years fro the baby snails to become mature

Evolution - Evolution - CephalopodsCephalopods

Advantages of evolution : the development of more

efficient swimming in response to increasing

competition from predatory fish

better locomotion moving the animal by jet

propulsion colour-changing cells in the

skin

Evolution - GastropodsEvolution - Gastropods

Reasons for evolution :

mechanical stability

defense against predators

sexual selectionclimatic selection

Type of gastropods :

semi-slugs slugs in various other

marine non-marine

gastropods

Human interactionHuman interactionpearls of bivalves and some

gastropodsSea silkTyrian purple dyeFood

SourcesSourcesWikipediaAnswer.comAndrewgrayYahoo!Advanced-level Biology for HK