1. Kingdom Animalia
Ch. 12- Phylum Mollusca

2. Key Characteristics of Mollusks
2nd largest animal phylum
Marine, freshwater, and terrestrial
Seven classes
True coelem- gut and internal organs suspend from body wall; cushioned by fluid
Trochophore- Free-swimming larval stage propels with cilia

3. Key Characteristics of Mollusks
Body cavity
Bilateral symmetry
3-part body plan:
Visceral mass- central section with organs
Mantle- Heavy fold of tissue forms outer layer of body
Foot- Muscular region for locomotion
Organ systems: Excretion, circulation, respiration, digestion, and reproduction
Shell- Exoskeleton made of protein, calcium carbonate, and hard minerals
Univalve- one part shell
Bivalve- two part shell
Radula- Tongue-like organ in mouth with thousands of backward-curving teeth in rows; Not in bivalves

4. Mollusk Body Plan

5. Organ Systems Excretion: Circulation: Coelem collects waste fluid
Nephridia- tubular structures recover useful molecules to be reabsorbed by tissues
Fluid waste leaves through pores in mantle
Circulation:
Digestive tube surrounded by mesoderm; barrier for diffusion of nutrients into tissues
Blood carries nutrients and oxygen to tissues and removes waste and carbon dioxide
3 chambered heart; open circulatory system
Exception: Octopus and squid; closed circulatory system

6. Organ Systems Respiration: Reproduction:
Most have gills; extract 50% or more oxygen
Sea snail gas exchange through skin
Terrestrial snails- no gills; thin moist membrane acts as primitive lung
Snails most active at night and after rain
When dry, pull into shell and plug opening with mucus
Reproduction:
Most distinct male and female individuals
Some snails and slugs hermaphrodites
Some oysters and sea slugs change back and forth from male to female
Octopus, freshwater snails, some freshwater mussels have no free-swimming larvae; juvenile stage hatches from egg

7. Class Gastropoda Snails and slugs Microscopic to 1 m in length
Mostly univalve; slugs and nudibranchs lost shell completely
Foot secretes mucus fro slimy path to glide on
Pair of tentacles on head with eyes on end
Herbivores use radula to scrape algae or tear leaves
Some active predators: sea slugs, whelks, and oyster drills (radula bores holes in other mollusk shells), and cone shells (use poison-tipped radula)
Whelks used by native-americans to make beaded wampum belts for trading or gifts to tribal leaders
Land snails, genus Helix, raised on snail farms for food
Few marine species, such as conchs, delicacies

8. Gastropods

9. Gastropods

10. Class Bivalvia Oysters, clams, scallops and mussels
Two-part hinged shell secreted by mantle
Adductor muscles- Connect valves and allow for opening and closing; water propels when snapped shut
No distinct head region nor radula
Nerve ganglion is simple brain; simple sense organs
Either male or female; few hermaphrodites
Sperm and egg release into water for fertilization
Trochophore larvae
Mussels brood in pouches on gills
Larvae are parasites on fish

11. Class Bivalvia
Filter feeders; cilia on gills draws water in through siphons (hollow tubes)
Mucus covering gills traps marine organisms and organic matter which is directed to the mouth
Mussels attach to rocks in intertidal zones
Scallops swim
Oysters permanently attach to rocks
Produce pearls when tiny foreign objects get trapped between mantle and shell
Coat them with nacre (mother-of-pearl) in successive layers
Fine pearls contain mineral crystals which act like prisms for color

12. Bivalves

13. Class Cephalopoda Squid, octopus, cuttlefish, and nautiluses
Squid, octopus, cuttlefish, and nautiluses
Body with large head attached to tentacles (foot divided into numerous parts)
Tentacles equipped with suction cups or hooks
Squids- 10 tentacles
Octopus- 8 tentacles
Nautilus- Between 80 and 90 tentacles
Lack an external shell; except nautilus
Squid and cuttlefish have small internal shell
Cuttlefish bones sometimes used in bird cages for calcium

14. Class Cephalopoda Most intelligent of all invertebrates
Complex nervous system with well-developed brain
Octopuses can be trained to classify objects; square from cross
Some have color vision
Squid have very large eyes for collecting light; Giant squid is largest invertebrate with largest animal eyes
Move by water propulsion
Some release dark fluid when threatened to conceal their escape
Cuttlefish ink used by many famous historical artists

15. Class Cephalopoda Active marine predators
Feed on fish, mollusks, crustaceans, and worms
Tentacles nab prey and pull into mouth
Strong, beak-like jaws tear apart
Radula pulls pieces into mouth
Blue-ringed octopus: Extremely poisonous

16. Cephalopods

17. Ammonites Extinct cephalopod Fossil records Had conical shell
Only living cephalopod is the nautilus

18. Squid vs. Octopus Squid Octopus 10 tentacles 8 tentacles Inner shell
No shell
Change color- camouflage
No ability to change color
Swim tentacles first
Swim head first

19. Class Caudofoveata Wormlike mollusks with cylindrical, shell-less body
Deep-water marine burrowers
No eyes
Chaetoderma

20. Class Aplacophora Shell, mantle and foot lacking Worm-like
Marine and burrowing
Neomenia

21. Class Monoplacophora Single, arched shell Broad, flat foot Marine
Neopilina

22. Class Scaphopoda Body enclosed in a tubular shell Open on both ends
No head
Tentacles used for deposit feeding
Dentalium

23. Class Polyplacophora Chitons Reduced head Flattened foot
Shell with eight articulating dorsal valves
Most feed on algae