1. Phylum Mollusca
“Soft Body”

2. Mollusca (Soft Body) 4 Major Classes Scaphopoda -- Tooth, tusk shell
Bivalvia (pelecypoda) -- Clams, mussels, oysters
Gastropoda -- Snails, conchs, welks
Cephalopoda -- Squids, octopus, nautili

3. Common Characteristics
Bilateral Symmetry - anterior head
Mantle - Secretes calcium carbonate shell (CaCo3)
Muscular Foot - Burrowing & crawling
Digestion: complete -
Mouth with radula (tongue with teeth)
Glands - liver & salivary
Circulatory - Generally open with dorsal heart and vessels

4. Common Characteristics cont.
Respiration - Gills (ctenidia), mantle (epidermis)
Excretory - Kidneys (nephridia)
Nervous system - Several pair of ganglia (cerebral, pedal, visceral) form connective nerve system
Reproduction - Sexes separate (dioecious) or together (monoecious). External sexual fertilization (oviparous)

5. Common Characteristics cont.
Free living, mostly aquatic (marine), some terrestrial
Economic importance - Food, jewelry (shells, pearls, etc), some negative impact...

6. Class Scaphopoda - “Tusk Shell”
Marine, burrow with foot into mud or sand
No head, lacks gills
Mantle absorbs oxygen from water
Ciliated, contractile tentacles surround mouth

7. Class Scaphopoda cont... No eyes or other distinct sensory organs
Several pair of ganglia form a coordinated sensory system
Uses captacula (tentacles extending from foot) to find food in sediment and carry it to the mouth
Reproduction - separate sexes - external fertilization. Fertilized egg develops into larvae

8. Class Bivalvia - “Two shells”
Clams, oysters, mussels, scallops - exoskeleton of two shells
AKA “pelecypoda” (hatchet foot)
Bilateral symmetry
No head
Filter feeders - no radula
Gills serve two purposes
Oxygen absorption
Food filtration

9. Bivalvia cont... Muscular foot Scallops can “swim”
Water flows through siphons
Incurrent - ventral
Excurrent - dorsal
Flow created by cilia

10. Bivalvia cont... Muscular system Adductors - close valves
Muscular foot operated by protractors & retractors
Respiration
Mantle; thin double gill
Aquatic
Some marine
Bottom dwellers

11. Bivalvia cont... Umbo - oldest part of the shell
Shell grows outward in concentric rings
Simple nervous system - no brain
Generally lack sensory organs
Scallops have complex eyes
Three chambered heart
Reproduction
Sexes generally separate
External fertilization (oviparous)

12. Gastropoda (Belly foot)
Largest, most diverse class: 40,000 living and 15,000 extinct species.
Snails, slugs, conchs
Generally bilateral symmetry

13. Gastropoda cont... Dorsal shell contains visceral mass
Univalve (CaCo3); Apex is central point of shell & is oldest. Successive layers are called whorls, formed around a central axis called columella

14. Gastropoda cont. Anterior head
Pair of tentacles, each with an “eye”
Radula used in feeding
Most important sensory organ are olfactory receptors, located at the tips of tentacles
Movement with muscular foot

15. Gastropoda cont.
Respiratory - Lungs in terrestrial species complete with network of blood vessels
Well developed, coordinated nervous system
Generally monoecious

16. Cephalopoda (head-foot)
Squids, octopus, nautili
Most developed mollusc
Large anterior head with 2 well developed eyes
Tentacles - suction cups located radially around mouth

17. Cephalopoda cont... Mouth - beak & radula
Foot - modified into a funnel-like siphon
Respiration
Circulation
Jet propulsion

18. Cephalopoda cont... Dioecious -- sexes separate
Internal sexual fertilization
Develop internal eggs, hatch into miniature which are able to feed & swim
Shell lacking or reduced to internal structure
In squid, “pen” is remnant of shell -- feather shape structure that supports mantle, serves as site for muscle attachment
Nautilus has external CaCo3 shell

19. Cephalopoda cont... Nervous system -- Brain with coordinated ganglia
Marine
Ink Sac -- self-defense mechanism
present in all cephalopods except Nautilus