Molluscs Zoe Wong 6s 27

Classification: Phylum: Mollusca The 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)

ClassExample Gastropod  chiton  limpet  periwinkle  snail Bivalve  mussel  oyster Cephalopod  squid  octopuse

Diversity vary from 50,000 to a maximum of 120,000 species in 2001 estimated about 93,000 named species Has been estimated that there are about 200,000 living species in total 70,000 fossil species 80% of all known mollusc species are gastropods

Characteristics 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 Structure 1 radula2 mouth 3 shell4 stomach 5 gonad6 heart 7 coelom8 nephridium 9 mantle10 mantle cavity 11 anus12 gill 13 foot14 hemecoel 15 pedal nerve cord16 gut 17 visceral nerve cord18 nerve ring

Reproduction can be sexual have both male and female reproductive organs mating happens during some particular time and temperature snail 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 eggs 14 days to hatch 2 years fro the baby snails to become mature

Evolution - Cephalopods 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 - Gastropods Reasons for evolution : mechanical stability defense against predators sexual selection climatic selection Type of gastropods : semi-slugs slugs in various other marine non-marine gastropods

Human interaction pearls of bivalves and some gastropods Sea silk Tyrian purple dye Food

Sources Wikipedia Answer.com Andrewgray Yahoo! Advanced-level Biology for HK