1. Gastropods, chitons, bivalves, cephalopods
Mollusca
Gastropods, chitons, bivalves, cephalopods

2. Characteristics Bilateral Soft-bodied Reduced coelom
Mantle – skirt-like extension of body mass
Not all have heads
Many have shells
Many have radula
Gills act as respiratory system

3. Gastropod = belly foots
Largest group – snails, sea slugs, nudibranchs, limpets
Only group to have anus near mouth, because of torsion during development

4. anus, which discharges wastes into mantle cavity
before torsion:
after torsion:
mouth
mouth
anus
mantle’s edge
anus, which discharges wastes into mantle cavity
Fig b, p.416

5. excretory organ gill anus heart mantle cavity digestive gland stomach
shell
mantle
foot
radula
Fig a, p.416

6. Circulation Open system
Respiratory pigment hemocyanin (colorless to blue)
The heart has one or more pairs of atria, receive oxygenated blood from the gills, pump it to the ventricle, which pumps it into the aorta
Cephalopods have a closed system

7. Excretory
atria of the heart also filter waste products out of the blood and dumping it into the coleom as urine.
Nephridia extracts any re-usable materials from the urine and dumps additional waste products into it, and then ejects it via tubes that discharge into the mantle cavity

8. Nervous system
Two pairs of main nerve cords – one serves internal organs and one the foot
Run below the gut and include ganglia as control centers
If they have a brain it encircles the esophagus

9. mouth
left mantle
retractor muscle (cut)
retractor muscle (cut)
Water flows out through exhalant siphon
Water flows in through inhalant siphon
foot
palps
left gill
shell
Fig b, p.417

10. Reproduction Simplest use external fertilization
All sexual reproduction
Can be hermaphrodites or dioecious

11. Skeleton/Movement Varies, depends on the structure of their foot
Gliding, jet propulsion

12. arm
jaw
internal shell
radula
mantle
anus
gill
reproductive organ
siphon
heart
ink sac
tentacle
accessory heart
Fig b, p.418