1. Mollusks
Chapter 16

2. Molluscs are triploblastic which means three tissue layers.
II.             Molluscs are coelomates:  a fluid filled body cavity lined by mesoderm.  Have a complete digestive system.

3. 2 Groups of coelomates: 1. Protostomes: Molluscs and Annelids
 Spiral, determinate cleavage
The blastopore forms the mouth

4. v Radial, indeterminate cleavage. v The blastopore forms the anus.
2.       Deuterostomes: echinoderms, chordates
v  Radial, indeterminate cleavage.
v  The blastopore forms the anus.

5. The coelom may have formed from splitting of the mesoderm or from out- pocketing of the gut.

6. Phylum Mollusca shares characteristics
III. 8 different classes  
Body composed of a head-foot and visceral mass (organ systems)
A mantle – covers visceral mass and may secrete a calcareous shell

7. Other common characteristics
Bilateral symmetry
Protostome characteristics
A trochophore larva
A reduced coelom
Open circulatory system
    (exception: cephalopods which have a closed      
     circulatory system)
Many molluscs feed via a radula

8. Herbivores, feeding with a radula Respiratory
Class
Gastropoda
Examples
Snails and Slugs
Feeding/digestion
Herbivores, feeding with a radula
Respiratory
Gills; mantle contractions circulate air; have a siphon which serves as an inhalant tube.
Circulatory
Open (blood flows from heart leaves the vessels and goes directly into sinuses.)
Skeletory
Hydraulic (blood confined to tissue spaces for support.)
Nervous system
6 ganglia in the head foot and a visceral mass
a.    eyes on tentacles
b.   statocysts on the foot for equilibrium
c.    ophradia in the anterior wall of the mantle that helps detect prey.
Excretory
Nephridium – converts ammonia to uric acid

9. Reproduction
External fertilization with some being monoecious and others being dioecious.
Locomotion
A ciliated, flattened foot covered with glands used to creep across the substrate.
Special Features
Torsion – gives shell the coiled appearance

10. Bivalvia Examples Clams, oysters, mussels, and scallops
Class
Bivalvia
Examples
Clams, oysters, mussels, and scallops
Feeding/digestion
Filter-feeders; loss of head and radula
Respiratory
Cilia covered gills forming folded sheets called lamellae; cilia moves water over an incurrent siphon
Circulatory
Open
Skeletory
External shell
Nervous system
3 pairs of ganglia, sensory cells on the margin of the mantle, photoreceptors, statocysts and osphradium
Excretory
Nephridium
Reproduction
Most dioecious; external fertilization
Locomotion
Sedentary
Special Features
Two convex halves of shell called valves

11. Cephalopoda Class Examples Octopuses, squids, cuttlefish, and nautili
Feeding/digestion
Locate prey by sight and capture prey with tentacles that have adhesive cups; radula and beak for tearing food; peristalsis replaces ciliary action

12. Respiratory
Gills
Circulatory
Closed – blood confined to vessels; more efficient
Skeletory
Shell is reduced or absent; except nautilus
Nervous system
Large brain – memory and decision making; can form images, distinguish shape & some color; statocysts by brain; osphradia only in nautilus
Excretory
Have a kidney which allows waste to filter directly from the blood stream which is very efficient
Reproduction
Dioecious; males have a hectocotylus for spermatophore transfer into the female near the opening of the oviduct; eggs deposited onto a substrate and hatchlings are miniature adults.
Locomotion
Jet propulsion (water forced through funnel)
Special Features
Modified foot into tentacles or arms.  They have chromatophores (pigment cells) which allow animal to change color and discharge ink for defense; confuses predator allowing the cephalopod to escape.