1. CLAMS,SQUIDS, OCTOPUSES, SNAILS, SLUGS, ETC.
PHYLUM MOLLUSCA
CLAMS,SQUIDS, OCTOPUSES, SNAILS, SLUGS, ETC.

2. General Characteristics
More than 100,000 species
“soft bodied”
Bilaterally symetrical
Trochophore larva
3 main body parts
Mantle: thin membrane that surrounds the visceral mass, and secretes shell
Visceral mass: digestion, excretion, and reproductive organs
Head-foot: sense organs, mouth, and is used for locomotion

3. 5 Major Classes of Mollusks
Class Amphineura (Polyplacophora) – Chitons
8 calcareous plates on their dorsal surface
Feed by grazing on algae along rocky intertidal zones
Class Scaphopoda – Tusk Shells
Elongated shell open at both ends that resemble elephant tusks
Live in sandy or muddy bottoms
Feed by extending tentacles into surrounding sediment or water

4. Class Gastropoda – Snails, slugs, nudibranchs, limpets, etc
Class Gastropoda – Snails, slugs, nudibranchs, limpets, etc. (90,000+ species)
Single shelled or no shell
Means “stomach (or belly) foot”
Body undergoes torsion - 180º rotation of internal organs, so that the anus ends up behind the head and waste products can exit the shell
Radula for feeding
Two types: one for scraping found in herbivores and one that is piercing found in carnivores
Many have an opercula – trap door that closes off the shell for protection made of chitin

5. Class Bivalvia (Pelecypoda) – clams, mussels, oysters, scallops, etc.
Two shells that they can close tightly for protection
Filter feeders that brings in water and food using a siphon
Some are burrowers, others attach themselves to rocks (most are sedentary)
Some can manufacture pearls by secreting nacre to coat irritating particles

6. Class Cephalopoda – squids, octopuses, cuttlefish, and nautilus
“head foot” because the feet (tentacles) are attached to the head
Shell is either reduced (internal pen) or absent in all except for the nautilus
Fast moving predators that use “jet” propulsion by expelling water through a siphon
Mouth with a beak for feeding on fish
Major types:
Squid: 8 short arms and 2 long feeding tentacles
Octopus: 8 arms
Cuttle fish: 10 arms
Nautilus: only one with external shell