1. Phylum Mollusca
November 3-4, 2014

2. Chiton
Conch
Clams, Oysters
Nudibranch
Octopus
Squid

3. General Characteristics
Soft-bodied invertebrates
Unsegmented body, typically bilateral symmetry
Internal or external calcium carbonate shell (usually)
Second largest animal phylum
~ 200,000 species
Show Cephalization
Sensory organs towards one end of body
“head” formation
Habitat/Lifestyle
Sessile-mobile
Benthic-pelagic
Predators-Herbivores-deposit feeders-filter feeders

4. Typical Body Plan of Mollusks
Three main parts:
Foot
Mantle
Shell
Foot:
On ventral side
muscular; used for crawling, burrowing, or capturing prey
Can be flat (snails)
spade-shaped (clams)
or modified into tentacles (squid and octopus)
Abalone

5. Body Plan of Mollusks Body covered with protective mantle: Shell:
Thin layer of tissue that covers most of the mollusk’s body
May or may not produce a shell
Shell:
made by glands in mantle that secrete calcium carbonate

6. Feeding with Radula
Diverse: herbivores, carnivores, filter feeders, detritivores.
Some use Radula for feeding
Radula: flexible, tongue-shaped structure covered with tiny teeth
Herbivores use radula to scrape or cut algae; carnivores use radula to drill through shells or flesh.

7. Radula
Fig. 16.3

8. Filter Feeding
Clams, oysters, and scallops filter feed using feathery gills
Mucus produced by gills traps plankton as water comes in through siphons

9. Mollusc Reproduction & Development
Sexual reproduction, external
In tentacled species, fertilization is internal and female lays fertilized eggs
Most have separate sexes that cross-fertilize eggs
Some hermaphrodites-both sexes
Larval stages
Trochophore larva
Free swimming, ciliated, shell formation begins
Veliger larva
Free swimming

10. Veliger
Zygote
Trochophore
Juvenile
Adult
Spat

11. Respiration Aquatic species use gills inside mantle to exchange gases
Incurrent and excurrent siphon brings water in
Siphon:
Tube-like structure through which water enters and leaves

12. 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

13. 6 Classes in Phylum Mollusca
1)Monoplacophora-simple hat shaped shells
2)Polyplacophora----chitons, 8 overlapping shells
3)Scaphopoda-tusk shells
4) Gastropoda-snails, slugs, nudibranchs, and conchs, limpets, abalone
4) Bilvalvia - clams, oysters, scallops, and mussels
5) Cephalopoda squid, octopus, and nautilus

14. Class Gastropoda “Stomach footed” molluscs
Have a single shell (snails) or no shell (slugs)

15. Class Gastropoda-the shells you find!
Snails, abalone, limpets, slugs, nudibranchs
Most varied of all molluscs
Marine, freshwater, or terrestrial
Aquatic snails breathe through gills
Use radula to scrape algae for food
Retreat into shell in dry periods & seals opening with mucus
Have open circulatory system
Secrete mucus & use muscular foot to move

16. Class Gastropoda
NUDIBRANCHS
Marine slug
Lacks shell

17. Class Gastropoda NUDIBRANCHS
Feed on sponges Cnidaria, algae
Exposed feathery gills
Can be toxic
Retain undigested nematocysts from Cnidaria=Kleptoplasty

18. Class Bivalvia, Bi-valve = two shells
two-part, hinged shell
Ex: clams, oysters, scallops
mussels
Most sessile, benthic
Most are filter feeders
No head or radula
Burrow
Sand, wood, rocks
A few can use muscular foot that extends from shell for movement
Scallops clap valves together to move

19. Class Bivalvia Shell secreted by mantle
Oldest, raised part of shell called umbo
Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen
Have heart & open circulatory system

20. Class Cephalopoda Octopus, squid, cuttlefish, & chambered nautilus
Move by using mantle cavity as jet propulsion
Sucks water into mantle cavity, pushes water out of muscular siphon that can change size (speed) and direction.  
Most intelligent mollusk
Well developed head –centralized brain
Large eyes, visual predators
Lack outer shell, very flexible
Active, free swimming predators
Foot divided into tentacles with suckers   

21. Class Cephalopoda
Chromatophores: can change color, used for camoflauge and social signaling.
1st group with social signaling-reguires more complex brain to interpret signals
Use their radula & beak to feed
Closed circulatory system
Highly developed nervous system with vertebrate-like eyes
Sexual reproduction
Separate sexes with internal fertilization

22. Class Cephalopoda SQUID Largest invertebrate is the Giant Squid
Large, complex brain
8 tentacles 2 arms- longer pair to catch prey
Use jet propulsion
Chromatophores
Have internal shell called pen

24. Class Cephalopoda
Can squirt an inky substance into water to temporarily blind predators

25. Class Cephalopoda OCTOPUS Eight tentacles Similar to squid
Sit & wait predators = ambush
Female dies after tending to eggs.
Beak like jaws, radula

26. Importance of Mollusks
Filter water, healthy waters
Keep algae growth done
Food for top predators and economically important species.
Used  by humans for food
Pearls from oysters
Shells used for jewelry