1. Phylum Mollusca
p. 585

2. Characteristics Means “soft-bodied” 2nd largest phylum of animals
Live everywhere
1mm  20 metres
Bilateral symmetry
Coelomate
Body plan:
Foot – sensory organs & muscles
Mantle – secretes shell
Shell (CaCO3) – protection & support
Visceral mass – digestive, reproductive, & circulatory organs

5. Classes include: Gastropoda – most have 1 shell (snails, slugs)
Bivalva - 2 shells (clams, oysters, mussels)
Cephalopoda - small internal shell (squid, octopus)
Polyplacophora – 8 rows of articulating plates (chitons)

6. Body Systems Digestive System: Mobility: Complete
Free-living & parasitic forms
Most use radula (tongue-shaped feeding organ)
Bivalvia use gills to filter feed
Mobility:
Bivalvia – mostly sessile
Gastropoda – use muscular foot
Cephalopoda – muscularized mantle & siphon for jet propulsion

8. Excretion: Response: Anus for solid waste
Nephridia for metabolic wastes
Response:
Varied depending on class
Bivalvia: simple nervous system & sense organs
Gastropoda: nerve ring & nerve cords
Cephalopoda: very complex nervous system & highly developed sense organs (for example: well developed brain & eyes); can learn
Blue-ringed octopus
deadliest octopus
No more than 8 inches
Venom is 10,000 times more powerful than cyanide
Enough venom to kill nearly 30 humans within a matter of minutes

9. Reproduction: Sexual Bivalvia – separate sexes; external fertilization
Gastropoda – hermaphrodites; internal fertilization
Cephalopoda – separate sexes; courtship; internal fertilization
All show similar features during early development
For example: trochophore = a larva (see Fig p.586)

10. Circulation: All have system with heart & blood vessels
Cephalopoda - closed
Bivalvia & Gastropoda - open (has sinuses)

11. Respiration: Bivalvia – gills Gastropoda – diffusion
Cephalopoda – gills; O2 carried by hemoglobin

12. Ecological Roles
As a food source (squid, mussels, clams, oysters, octopus, snails)
Environmental monitor (but toxic if eaten!)
Medical research
Some molluscs do not develop cancer
Cosmetic products
Pearls
Damage crops/gardens
Shipworms destroy wooden ships/docks
“termites of the sea”