1. Mollusks Chapter 27-2 PHYLUM MOLLUSKA THE WORD MOLLUSK MEANS
“SOFT BODY”
MOLLUSKS ARE SOFT BODIED INVERTEBRATES.
But these are hard shells.!!!!***
Where’s the “beef”???

2. ANIMAL CLASSIFICATION

3. CHARACTERISTICS OF MOLLUSKS
SOFT BODY COVERED BY A FOLD OF TISSUE CALLED A MANTLE
HEAD AND A MUSCULAR FOOT FOR MOVEMENT

4. 4 Characteristics of Mollusks
All Mollusks have:
Muscular foot - used for locomotion
Mantle – thin, delicate tissue that covers the body of the mollusk, like a cloak
Shell – usually CaCO3, and secreted by mantle
Visceral mass – just below mantle, containing the internal organs

5. Foot of a Clam

6. Foot, Shell, Mantle, Visceral Mass are always Present in Mollusks

7. MOLLUSKS ARE GROUPED INTO 3 CLASSES ACCORDING TO THE TYPE OF FOOT
SHELL / NO SHELL
KIND OF SHELL

8. 2 CLASSES WITH SHELLS OUTSIDE THE BODY
UNIVALVE
(ONE SHELLED MOLLUSK)
BIVALVE
(TWO SHELLED MOLLUSK)

9. 3RD CLASS HAS NO SHELL
INSIDE OR
OUT

10. OCTOPUS

11. SQUID

12. The All Important COELOM is alive and well in the Mollusks.
Here’s why it’s important…
The development of a coelom allows for the formation of more complex tissues and organs.
It also allowed for a wide variety of body architectures; which allows for coelomates to grow larger.

13. The primary means of locomotion is via a muscular FOOT.
Sometimes the foot is modified, but it is always present.
Mollusks have a definite “head” region that contains organs for chemo-sensory functions.
All mollusks, except bivalves, possess a rasping tongue organ called the RADULA.

14. Anatomy of the Rasping Tongue, or Radula of a Snail

15. Function of the Radula
A layer of flexible skin, with hundred of sandpapery teeth, used to scrape algae off of rocks
In full-on carnivore mode, the radula acts like a drill to pierce shells. These things even have poison glands to make things nastier Octopi and certain sea slugs do this.

17. Bivalves are Usually Filter Feeders
Think “Clam” when Bleecker says Bivalve.
Come on, say it out loud now 
Feathery Gills are extended from Sessile, or virtually motionless bivalves to screen the water for microorganisms and algae to munch on

18. Bleecker Swam up to one of these in Hanauma Bay, on Oahu (Hawaii, people!)

19. Respiration
Gills are used, and have many capillaries to permit diffusion of O2 into blood stream
Gills on the Nudibranch are particularly cool 

21. Circulatory System
Open Circulatory System – the blood does not always travel in blood vessels, and often deposits into spaces or sinuses to drain back once organs have been bathed with blood
This works for clams and snails, but not highly motile octopi or squid, which have Closed Circulatory Systems

22. Excretion- Waste Management 101
2 openings in the digestive tract
Ammonia wastes from protein digestion can be toxic, and are eliminated via Nephridia, simple tube shaped organs leading out of the body, via the skin.

23. Reproduction
In a watery environment, egg and sperm are often released in mass quantities in hopes of fertilization. Larvae then swim to a spot on the bottom and grow into bivalves, etc.
In tentacled mollusks, modified tentacles are used in Internal Fertilization.
Spontaneous sex changes do occur, if there are not enough members of a given sex. Holy cross dressing Batman!

24. Classifying Mollusks Further
Class Gastropoda – stomach foot
Broad muscular foot on stomach side
Snails, Slugs, Nudibranchs
Some shelled, others not
Snail Shell shows RADIAL TORSION, creating the distinct spiral shape

25. Two Shelled Mollusks – Class Bivalvia
Oysters, Scallops, Clams, Mussels
Free swimming larvae
Mantle manufactures the shell
Pearls occur when a sand grain or foreign particle is covered in “mother of pearl”, a material used to keep the inside of the shell smooth

26. The Pearl Emerges – Black is Particularly Rare 

27. Classifying Mollusks Further
Class Cephalopoda – “head foot”
High degree of CEPHALIZATION
Octopi, Squid, Nautilus, Cuttlefish
Tentacled and highly motile, with excellent senses, particularly the eyes
Originated 500 million years ago, in Cambrian Period
No shell, but internal shell is present
Jet propulsion
Ink defense mechanism, Poisonous radula – ewww!

28. Bleecker-Vision!
The Nautilus

31. Bioluminescence! Complicated Chemical Reactions!

32. Ecological Role Food source – clams, oysters, squid, octopi
Filter feeders remove pollutants
Indicators of pollution
Ships worn down by bivalves
Recyclers of waste or detritus