1. Phylum Molluska

2. 3 Main Classes of Mollusks
GASTROPODA : includes limpets, snails, slugs and whelks
BIVALVIA: includes clams, oysters, muscles, scallops and shipworms
CEPHALOPODA: includes octopi, squid, cuttlefish, nautilus and argonauts
Above: Limpet
Above: Scallop showing off its eyes!
Left: Cuttlefish and squid

3. All forms of Mollusks have a body composed of at least three distinct parts:
Visceral Mass
- The soft bodied portion that contains the internal organs
Foot
- A strong, muscular portion used for locomotion which is adapted as tentacles in cephalopods
Mantle
A membranous, sometimes muscular covering that envelops but does not completely enclose the visceral mass
Can secrete a shell
Illustration of the general features of all mollusks

4. Identifying Characteristics of Mollusks
Have a coelom which allows for specialization of organ systems
Most are bilaterally symmetrical
All have a visceral mass, foot and mantle (see previous slide)
Possess a one way digestive system with specialized organs and have feeding mouthparts
Cephalopods have a closed circulatory system, all other classes possess open circulatory systems

5. Identifying Characteristics of Mollusks
Many have highly developed cephalization with sensory organs
Many have calcium carbonate external shells
Respiratory system includes the use of gills to extract O2 and get rid of waste
Many have a radula which is a chitinous tongue used for feeding
Sexual Reproduction (have separate sexes: dioecious)

6. The Gastropods : “belly” “foot”
Usually are univalves (one shell)
Large, muscular foot
Well defined head
Muscles move in a rippling motion for movement
Most possess gills but some have lungs
Have a radula to help obtain food
Most snails have a lid-like part called an operculum on the back of the foot so they can draw their bodies into their shell and close off the opening
Underside of a Limpet

7. Gastropods in Love….
.. and a lonely garden slug….

8. The Bivalves : “two” “shell”
Possess 2 shells that can be tightly closed with strong muscles
Strong, muscular foot and use it for locomotion
No head or teeth
Obtain food and oxygen by using a muscular siphon that brings water to the gills which filter out O2 and plant cell material
Often attach themselves to surfaces
Possess an open circulatory system
GIANT CLAM

10. Above left: Elephant trunk clams, named for their large foot
Above right: an opened oyster commonly enjoyed raw or cooked as a delicacy
Lower right: Scallop showing off its many primitive eyes

11. The Cephalopods: “head” “foot”
Bilaterally symmetrical
Prominent head, arms and tentacles
Have developed brain “intelligent “ creatures
Arms that take in food surround a hard, strong, beak-like jaws that tear the prey and secrete a poison to paralyze it
Closed circulatory system with hemocyanin (like hemoglobin)
Move by jet propulsion
Can change color with the use of chromatophores
Possess advanced vision
Secrete an ink cloud when in danger

13. Squid Caribbean Reef Squid Tentacles of a giant squid
Calamari: a deep fried squid dish
Squid eye and gills

15. Octopus Octopus on the beach Octopus beak Swimming Octopus
Octopus arm in detail

16. Scientists are surprised to encounter what may be a never before seen octopus more than 4,000 meters (13,123 feet) deep in the sea near Hawaii. Video courtesy NOAA Office of Ocean Exploration and Research

17. Octopi are extremely intelligent creatures and have been known to learn to escape from their aquariums when in captivity through very small cracks at the top.

18. What is octopus ink?

19. Ecological Roles of Mollusks
Mollusks are part of the aquatic food chain (see picture to left)
Many mollusks are keystone species, if their numbers decrease the decline in other species of marine life will follow
Filter feeders help to purify the water
Many bivalves are reef forming and provide an ecosystem for other aquatic species
Reef builders stabilize banks and bottom sediments
Starfish eating (digesting) a mussel

21. Squid Fact
The largest squid ever caught was a 10 m long Colossal Squid off the coast of New Zealand and weighed in at 495 kg. Colossal Squid are larger than the giant squid found off the Mexican coast and are thought to grow in size to a whopping 13 meters!