1. Phylum Mollusca
Class: Gastropoda
Class: Bivalvia

2. Characteristics of Mollusca
• Protosome characteristics
• Coelom surrounds heart
• Open circulatory system (except cephalopods)

3. Class Gastropoda
Snails, Limpets and Slugs

4. Gastropoda
• Planning on being rich
and famous?
• Wining and dining at the
most expensive
restaurants?
• Romantic trips to Paris?
• Ever wonder what
Ceaser munched on
after long hard days
ruling the roman
empire?
• Than you should be
familiar with
ESCARGOT!!!!

5. General Body Plan:
Gastropod
• 1. Head foot
• Head: sensory
nerves, mouth
– Anterior: near the
head/mouth
• Foot: attachment and
locomotion
– Posterior: near the anus
– Flattened w Cilia:
locomotion

6. That slimy foot…
• Snail Slime:
– Suction power: travel up
and down trees
– Escape: Emit a nasty
tasting slime when
threatened
– Movement: Allows them
to easily squeeze
through tight spaces
– Water Retention
• Ecological Roles:
– Skin regenerating
– used in skin beauty
products

7. General Body Plan:
Gastropod
• 2. Visceral Mass
– Organs of
digestion
– Circulation
– Reproduction
– Excretion
– Dorsal to the
head foot

8. General Body Plan:
Gastropod
• Mantle (shell)
– Attached to visceral
mass
• Encloses most of the
body
– Protection
• Mantle Cavity:
– Gas exchange
– Elimination of digestive
wastes
– Release of reproductive
products

9. Respiration
• One Gill in mantle
cavity
– Oxygen is taken in
– Diffused through the cells
• Open Circulatory
System
– Pushes blood in to
expand
– Pulls it out to contract

10. General Body Plan: Mollusca
• Radula: Scraping
mouth
– Chitinous belt & curved
teeth
• Covers fleshy tongue
• Muscles move it back
and forth
• Conveyor belt
• Digestion
– Scrape algae
– Enzymes break down
food in stomach

11. • How do mollusks exchange gasses
– Filter air through their gills
• Where are these gills located?
– The mantel
• What is the structure called that scrapes up
food?
– A Radula
• All mollusks have:
– A visceral Mass
– A head foot
– A mantel

12. Gastropoda
• Marine, Freshwater, Terrestrial
• Signifying feature: Torsion

13. Torsion
• Benefits
– Head enters first:
protection
– Operculum seals
opening to prevent
drying out
– Allows clean water to
enter mantle cavity
– Makes snail more
sensitive to stimuli
coming from the front

14. Torsion

15. Reproduction
• Monoecious: can be
whatever sex they
want!
– Internal cross
fertilization
– One snail acts as
female one acts as
male
– Deposit eggs in
gelationous strings

16. CFU
• What is Torsion?
– The 180 degree twisting of internal organs
in snails
• How is Torsion adaptive?
– Pulls head in first, seals opening, locates
all sensory nerves in the front

17. Class Bivalvia
Clams, Oysters, Mussles, Scallop
s

18. Bivalvia!
• Edible
• Commercial value:
Form Pearls
• Valuable in removing
bacteria from polluted
water!
– Rely on water currents to
get food
– Filter in nutrients, filter
out clean water
• Valuable food source:
humans, raccoons,
otters, birds

19. Structure
• Two halves of a shell:
Valves
– Adductor muscles hold
valves shut
• Visceral Mass
• Mantel Cavity
• Gills
• Cilia
• Siphon:
– filters water in and out of
shell

20. Foot
• Most mollusks have
foot that can be
used differently
– Attach mollusk to
surface
– Act as a lure to
attract prey
– Surround organs for
safety

21. Respiratory System
• Respiration: Cilia in
gills move water into
mantel cavity
– Water tubes
exchange water to
blood through
diffusion
– Water exits bivalve

22. Digestive System
• Food comes in
through gills
– Sorted
– Digested
– Waste forcibly
pushed out of mantel
cavity by valves
shutting quickly

23. Human Interaction
• Many, many
mollusks are
threatened or
endangered
– Over harvesting
– Pollution
– Loss of habitat
– Loss of water
currents

24. CFU
• What is the technical term for the two halves
of the shell?
– Valves
• What structure filters water in and out of the
shell
– Siphon
• What is the function of the foot
– Attach mollusk to substrate, act as lure
• Why are bivalves important to humans?
– Pearls, food source, pollution filter
• How are humans affecting bivalves?
– Over harvesting, pollution, loss of current

25. Get ready for dissection!