1. Unit 7 opener #2 10/31
Shells are designed to protect the soft bodies of mollusks. How do unshelled mollusks defend themselves? What are some of their adaptations for defense?

2. PHYLUM MOLLUSCA

3. IIIb. Class Bivalvia
Clams, oysters, mussels, scallops.
All marine or freshwater
Second largest class
All have 2 shells

4. A. Locomotion Clams/mussels- muscular foot for burrowing
Oysters- adults are sessile
3. Scallops- “clap” shell

5. B. Shell Features 1. Shell structure
Periostracum
Prismatic
1. Shell structure
a. Periostracum- thin outer layer of protein
b. Prismatic layer- thick middle layer of calcium carbonate
c. Nacreous layer- inner layer; secretes nacre which forms pearls in some.
Nacreous

6. 3. Umbo- swollen area near anterior, dorsal end of clam; oldest part of shell.
4. Hinge ligament- holds two shells together
5. Growth lines- wider lines indicate more growth/better feeding season.
6. Anterior and Posterior adductor muscles- very strong muscles for opening or closing shell.

7. C. Digestion/Feeding 1. Filter feeders- algae, larvae, small particles
2. Food/water enter incurrent siphon.
3. Food swept into mouth by 2 pairs of palps
4. Esophagus, stomach, intestine, anus
5. feces/excess water leave thru excurrent siphon.

8. D. Respiration Oxygenated water enters incurrent siphon.
Gills have tubes where water & blood are close together. Gases exchange by diffusion across the membrane.
3. Deoxygenated water leaves thru excurrent siphon.

9. E. Circulation
1. Open
2. Heart and short vessels similar to gastropods.

10. F. Excretion 1. Nephridium Nervous/Sensory System
1. Ganglia concentrated in foot, esophagus, adductor muscle and mantle.
2. Some have eyes for sensing light around shell rim.
3. Osphradia- chemoreceptors

11. H. Reproduction 1. Most are dioecious- external fertilization
2. Sperm leave thru excurrent siphon
3. Sperm brought in thru incurrent siphon of female.
4. Clams release trochophore larvae which develop into adults.

12. 5. Mussels release glochidia which look like miniature adults.
These are usually parasitic on fish.
Attach to fish gills & feed on blood.
When adult organs form, they drop off & take on filter feeding life style.

13. Economic/Environmental Significance
1. Source of food/part of food chain
2. Filter/clean water of harmful pollutants (algae)- can cause sickness if red tide algae are eaten.
3. Form pearls/jewelry
4. Mother of pearl buttons made from shells

15. IIIc. Class Cephalopoda
Squid, octopus, nautilus, cuttlefish
All marine
Most complex mollusk
No external shell, have internal support
a. Squid- have internal chitinous structure called pen

16. b. Cuttlefish- have cuttlebone. Can be
b. Cuttlefish- have cuttlebone. Can be used as calcium supplement for birds.
c. Chambered nautilus-
has true shell

17. d. Octopus- has no shell

18. Dorsal
Anterior View
Fin
Mantle
Chromatophores
Water Jet
Eye
Arm
Tentacle
suckers
Ventral

19. Locomotion
1. All cephalopods can
move by jet propulsion-
forcefully expelling water from siphons on head.
2. Octopus crawl with arms.
3. Squid & cuttlefish have posterior fins for steering/movement.

20. 1. Have arms with suction cups to capture/hold prey.
Digestion/Feeding
1. Have arms with suction cups to capture/hold prey.
2. Sharp beak for tearing into prey.
3. Radula for drilling holes in shells.
4. Use extracellular digestion- secrete enzymes that breaks down food before enters mouth.
5. mouth, esophagus, stomach (cecum = digestive gland), intestine, anus, siphon
6. Most nocturnal- eat
crustaceans, fish,
other mollusks, etc.
Radula
Beak

22. Holes created by octopus radula.
“b” indicates where octopus gave up and used beak to break into shell.

23. Respiratory System
1. Gills in mantle cavity
Circulatory System
Closed- blood enclosed in blood vessels.
Have hemocyanin- copper rich blood (blue)
Excretory system
1. Nephridia

24. Nervous/Sensory System
1. Large brains- good memory, can work thru problems.
2. Complex eye- very similar to human eye. Can form images and distinguish color

25. Camouflage
a. Chromatophores- pigments cells in skin which allow color change. Can also use to communicate with other cephalopods (mating, aggression, fear, etc)
b. Suckers on arms are very sensitive. Can change texture of skin to match rocks.

26. Ink gland
ejects ink cloud when disturbed to make quick getaway.
tyrosinase- also released to irritate predators eyes and paralyze sense of smell

27. G. Reproduction Dioecious
Eggs are deposited in string-like masses in octopus den.
Octopus brood young until they hatch. Keeping clean of debris.
Young never cared for after hatching.

28. Cecum
Fin
Testis
Vena Cava
Branchial heart
Gill
Ink sac
Funnel
Tentacle
Arms
Eye
Intestine
Penis
mantle

29. Economic/Environmental Significance
1. Food source- calamari, octopus
2. Bait for commercial fishermen
3. Can be pests in oyster beds- eating up all profit!
4. Cephalotoxin may be used for medicine/research

30. The Giant Squid 50 feet long & weigh almost 1 ton
Eats fish & other squid and has been known to eat sperm whale calves