1. Invertebrates: Phylum Mollusca
Molluscs
Large and diverse group
Coelomates
Bilateral symmetry, three germ layers, organ level of organization, tube-within-a- tube body plan

2. Mollusca cont’d 3 body parts Visceral mass Head/Foot Mantle
includes most organs
Head/Foot
Radula: rasping organ for feeding
muscular portion used for locomotion
Mantle
covering that envelopes visceral mass
Mantle cavity: space between the two folds of the mantle
Mantle may secrete a shell

3. Diversity of molluscs
Fig

4. Mollusca cont’d Class Gastropoda Foot is flattened ventrally
Gastro= stomach Poda = foot
Foot is flattened ventrally
Nudibranchs
sea slugs, lack shell
Conchs & snails
have a shell
Protection, prevents dessication in land snails
Aquatic gastropods: have gills,
Terrestrial gastropods:mantle has lung-like function

5. Mollusca cont’d Class Cephalopoda Squid, octopus, Chambered nautilus
Cephalo = brain poda = foot
Squid, octopus, Chambered nautilus
Body Structure
Foot forms tentacles
Powerful beak and radula for feeding
Extremely well-developed eyes; complex behaviors
Ink glands- secrete “ink”as defense mechanism

6. Gastropod and cephalopod anatomy
Fig

7. Molluscs cont’d Class Bivalva Clams, oysters, scallops
Bi = two valva= shells
Clams, oysters, scallops
Gills enclosed in mantle cavity
Filter-feeders- water enters through incurrent siphon
Visceral mass
coelom is reduced-pericardial cavity is the only remains of the coelom
Open circulatory system
blood not always in vessels
“sloshes” around in sinuses
Heart pumps blood to dorsal aorta and then to organs

8. Molluscs cont’d Class Bivalva cont’d Lack cephalization
nervous system consists of ganglia connected by nerves
Digestive system
labial palps, esophagus, stomach, intestine
Excretion by kidneys
Sexes separate, fertilization produces a trochophore larva

9. Clam, Anodonta
Fig

10. Comparison of clam to squid to land snail
Table 30.2