1. Phylum Mollusca Chapter 12

2. Phylum Mollusca “soft”
Three Main Classes
Class Gastropoda (snails, slugs, limpets)
Class Bivalvia (muscles, clams, oysters)
Class Cephalopoda (octopus, squid, nautilus, cuttlefish)
Limpets

3. Body Form Bilateral Symmetry Invertebrate - no backbone
Hydrostatic Skeleton (fluid under pressure)
Triploblastic
Coelomate
1st animals to posses a coelom
Yes, even before annelids…
Small cavity; surrounds heart, nephridia, gonads
Protostomate
Blastopore become mouth – ‘primitive’

4. Functions of the Coelom
Provides room for organ development
Surface diffusion of
Gases
Nutrients
Wastes
Storage
Elimination of reproductive products
Hydrostatic support

5. Characteristics of Molluscs
Size: <1cm – 18m
Garden slug – Giant squid
3 Body Regions
Mantle – tissue that covers the body
May secret a shell
Fxn: excretion, gas exchange, elimination of wastes, reproductive products
Visceral mass – contains organs
Head foot – elongate foot w/ anterior head

6. Characteristics of Molluscs (cont.)
Open circulatory system in all except cephalopods
Radula – rasping/scraping structure
Covers tonguelike structure

7. Class Gastropoda Snails, limpets, slugs
Over 35,000 species <Largest class>
Habitat: Marine, freshwater, terrestrial
Operculum ‘lid’
Dorsal posterior end
Used for protection from predators & desiccation
6th Hr Left off Here 3/7/14

8. Class Gastropoda Undergo Torsion during larval stage-
180° Twist of visceral mass & mantle
Allows head to enter shell first for protection
Allows for clean water in front of the snail to enter mantle cavity
Makes snail more sensitive to stimuli coming from the direction in which it moves

9. Class Gastropoda Locomotion Flattened foot Cilia over mucous trail
Sometimes ciliated
Muscular contractions
Cilia over mucous trail

10. Class Gastropoda Nervous Communication Ospharidia
Chemoreceptors
Detect sediment & chemicals in inhalant H20
Helps detect prey
Ganglia linked by nerves
base or end of tentacles
Photo receptors
Lens & Cornea
Statocysts in the foot (balance)
5th Hr. Left off Here 3/7/14

11. Class Gastropoda Cardiovascular: Respiration Open Circulatory System
Blood “hemolymph” leaves blood vessels
Blood bathes tissue directly in hemocoel ‘sinus’
Function of blood: transport nutrients, wastes, & gasses
Respiration
Gills
Diffusion of O2 across mantle

12. Class Gastropoda Digestion Food trapped in mucus strings
Gets incorporated into protostyle
Protostyle – rotating ‘mucoid mass’ in gut of gastropod
Radula
Ciliated digestive tract
2nd Hour Left off Here

13. Class Gastropoda Excretory Waste Removal
Wastes excreted through coelom from blood
Aquatic – produce ammonia
Terrestrial – produce uric acid (less toxic) – conserves water
Nepheridium – excretory organ

14. Class Gastropoda Reproduction Marine snails – external fertilization
Dioecious
Gametes discharged into sea
Freshwater & Terrestrial snails – internal fertilization
Monecious
Copulation - Exchange sperm
– or -
One snail may act as the male, the other as the female

15. Class Bivalvia “two-leaf”
Mussels, clams, oysters, scallops
Habitat: Marine, freshwater
Help remove bacteria from polluted water
2 convex halves- valves
Proteinaceous hinge

16. Class Bivalvia Tongue & grooves in shell to prevent twisting
Umbo – swollen area – looks like a notch
Oldest part of shell
Sheet like mantle

17. Class Bivalvia Muscular movement: Adductor muscles to close shell
Defense against predation
Sea stars can break this muscle
Steaming bivalves…
Sessile (immobile)

18. Class Bivalvia Nervous Communication 3 pairs of interconnected ganglia
Margin of the mantle is main sense organ
has sensory cells
Tentacles
Photo receptors or Lens & Cornea
Statocysts – balance/gravity
Osphraidium – chemoreceptors in mantle

19. Class Bivalvia Cardiovascular System Respiration
Open circulatory system
Blood flow:
heart  tissue sinuses  nepheridia  gills  heart
Respiration
Gills covered in cillia
diffusion

20. Class Bivalvia Digestive System Filter feeders
Gills trap food particles
Move down food grooves (ciliated tracts)
Labial palps sort food particles

21. Class Bivalvia Excretory System 2 Nepheridia Duct system
Nephridiopores in anterior region for excretion of wastes

22. Class Bivalvia Reproduction Most dioecious – male/female
Few monoecous – hermaphroditic
Most external fertilization
Spew out gametes and fertilize in sea
Some internal fertilization (fresh water only)
Female sucks in sperm from inhalent water
Young clams shed from gills

23. Class Cephalopoda

24. Class Cephalopoda “head foot”
Most complex mollusc
All except nautilus have a reduced shell
Cuttlefish & squid have internal shell
Nautilus has a coiled shell for support
Modified foot for food capture, attachment, locomotion, & reproduction
Visceral mass located in head segment

25. Class Cephalopoda Muscular movement Jet propulsion
Foot modified into tentacles

26. Class Cephalopoda Nervous Communication
Highly developed nervous system
Brains are large
Fusion of ganglia
Statocysts (gravity)
Eyes

27. Class Cephalopoda Cardiovascular 1st to have Closed circulatory system
Heart consists of 2 auricles and 1 ventricle
Have contractile arteries and branchial hearts
Respiration
Gills & diffusion

28. Class Cephalopoda Digestive System Jaws & Radula
Tentacles w/ adhesive cups or foot to capture prey
Feed on small invertebrates
Efficient predators