1. Phylum Mollusca

2. General Characteristics
Soft-bodied invertebrates
Internal or external shell
Second largest animal phylum
Include snails, slugs, clams, squids, and octopi
Fully-lined coelom
Show cephalization

3. General Characteristics
Free-swimming, larval stage called a trochophore
Development very similar to annelids which shows common ancestry
Bilaterally symmetrical
Most have separate sexes that cross-fertilize eggs
Gills between mantle and visceral mass used for gas exchange

4. General Characteristics
Includes four classes:
Polyplacophora (chitons)
Gastropoda (snails, slugs, nudibranchs, and conchs)
Bilvalvia or Pelecypoda (clams, oysters, and mussels)
Cephalopoda (squids, octopus, and nautilus)

5. Body Plan of Mollusks
Four main parts: foot, mantle, shell, and visceral mass
Foot: muscular; used for crawling, burrowing, or capturing prey
Can be flat (snails), spade-shaped (clams), or modified into tentacles (squid and octopus)

6. Body Plan of Mollusks
Body covered with protective mantle: thin layer of tissue that covers most of the mollusk’s body; may or may not produce a shell
Visceral mass: body organs lying below and protected by the mantle (all internal organs)
Shell: made by glands in mantle that secrete calcium carbonate

7. Feeding
Can be herbivores, carnivores, filter feeders, detritivores, or parasites
Snails and slugs use radula for feeding
Radula: flexible, tongue-shaped structure covered with tiny teeth
Herbivores use radula to scrape; carnivores use radula to drill through shells or flesh

8. Feeding Clams, oysters, and scallops filter feed using feathery gills
Mucus produced by gills traps plankton as water comes in through siphons
Siphon: tubelike structure through which water enters and leaves
Octopi and squid use tentacles and sharp bird like beak to capture and eat prey

9. Respiration Aquatic species use gills inside mantle to exchange gases
Terrestrial species use mantle cavity lined with blood vessels to capture air and exchange gases
Lining must be kept moist to allow for diffusion of oxygen and CO2 exchange

10. Circulation Can be open or closed circulatory system
Open system: blood is pumped by simple heart into sinuses (large saclike space) then to gills, then back to heart; slower system; found in snails and clams
Closed system: blood is pumped by heart through blood vessels; faster system; found in faster-moving mollusks

11. Excretion
Nitrogen-containing wastes (ammonia) is released from blood through nephridia

12. Response/Nervous System
Can be simple or very complex
Bivalves have small ganglia, few nerve cords, and simple sense organs
Cephalopods have well-developed brains, good memory, and complex eyes; Can be taught to do many tasks: open jar, perform for reward

13. Movement All use foot for movement
Snails/slugs use mucus and rippling motion of foot
Aquatic species use siphons to suck in water and shoot it out “jet propulsion”

14. Reproduction Sexual reproduction External fertilization
Release enormous amounts of eggs and sperm into water
Free swimming larvae
In tentacled species, fertilization is internal and female lays fertilized eggs

15. Class Polyplacophora Common name is chiton All marine
Shell divided into 8 over-lapping plates
Live on rocks along seashore
Feed on algae

16. Class Gastropoda
Head has a pair of retractable tentacles with eyes located at the ends
Have a single shell or valve (snails) or none (slugs)
Known as univalves

17. Class Gastropoda PTEROPODS Called "sea butterflies“ Marine
Have a wing-like flap for swimming

18. Class Gastropoda
NUDIBRANCHS
Marine slug
Lacks shell
Can be poisonous

19. Class Bivalvia Sessile or sedentary
Includes marine clams, oysters, & scallops and freshwater mussels
Filter feeders
Have two-part, hinged shell (2 valves)
Have muscular foot that extends from shell for movement
Scallops clap valves together to move

20. Class Bivalvia
Shell secreted by mantle & made of 3 layers --- outer horny layer protects against acids, middle prismatic layer made of calcium carbonate for strength, & inner pearly layer next to soft body
Mantle secretes substance called "mother of pearl" to surround irritants like grains of sand
Oldest, raised part of shell called umbo

21. Class Bivalvia
Powerful anterior & posterior adductor muscles open & close shell
No distinct head
Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen
Have heart & open circulatory system

22. Class Bivalvia
Nervous system made of 3 pairs of ganglia, nerve cords, & sensory cells that detect light, chemicals, & touch
Separate sexes with external fertilization of eggs

23. Class Cephalopoda
Includes octopus, squid, cuttlefish, & chambered nautilus  
All marine
Most intelligent mollusk
Well developed head
Active, free swimming predators
Foot divided into tentacles with suckers   

24. Class Cephalopoda Use their radula & beak to feed
Closed circulatory system
Lack external shell
Highly developed nervous system with vertebrate-like eyes
Separate sexes with internal fertilization

25. Class Cephalopoda SQUID Largest invertebrate is the Giant Squid
Large, complex brain
Ten tentacles with longest pair to catch prey
Use jet propulsion to move by forcing water out their excurrent siphon
Chromatophores in the skin can help change squid color for camouflage

26. Class Cephalopoda
Can squirt an inky substance into water to temporarily blind predators
Have internal shell called pen
Female lays eggs in jellylike material & protects them until hatching

27. Class Cephalopoda OCTOPUS Eight tentacles Similar to squid
Crawls along bottom looking for prey

28. Class Cephalopoda CHAMBERED NAUTILUS Has an exterior shell
Lives in the outer chamber of the shell
Secretes gas into the other chambers to adjust buoyancy

29. Economic Importance of Mollusks
Used  by humans for food
Pearls from oysters
Shells used for jewelry
Do crop & garden damage
Serve as intermediate hosts for some parasites such as flukes