2. Phylum Molluska www.onacd.ca

3. 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: Scallop showing off its eyes! Left: Cuttlefish and squid Above: Limpet

4. All forms of Mollusks have a body composed of at least three distinct parts: 1. Visceral Mass - A soft bodied portion that contains the internal organs 2. Foot - A strong, muscular portion used for locomotion (adapted as tentacles in cephalopods) 3. 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

5. Identifying Characteristics of Mollusks Have a coelom which allows for specialization of organ systems Have a coelom which allows for specialization of organ systems Most are bilaterally symmetrical Most are bilaterally symmetrical All have a visceral mass, foot and mantle (see previous slide) All have a visceral mass, foot and mantle (see previous slide) Possess a one-way digestive system with specialized organs and have feeding mouthparts 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 Cephalopods have a closed circulatory system, all other classes possess open circulatory systems Many have highly developed cephalization with sensory organs Many have highly developed cephalization with sensory organs Many have calcium carbonate external shells Many have calcium carbonate external shells Respiratory system includes the use of gills to extract O 2 and get rid of waste Respiratory system includes the use of gills to extract O 2 and get rid of waste Many have a radula which is a chitinous tongue used for feeding Many have a radula which is a chitinous tongue used for feeding Sexual Reproduction (have separate sexes: dioecious) Sexual Reproduction (have separate sexes: dioecious)

6. The Gastropods : “belly” “foot” Usually are univalves (one shell) Usually are univalves (one shell) Large, muscular foot Large, muscular foot Well defined head Well defined head Muscles move in a rippling motion for movement Muscles move in a rippling motion for movement Most possess gills but some have lungs Most possess gills but some have lungs Have a radula to help obtain food 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 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 Possess 2 shells that can be tightly closed with strong muscles Strong, muscular foot and use it for locomotion Strong, muscular foot and use it for locomotion No head or teeth No head or teeth Obtain food and oxygen by using a muscular siphon that brings water to the gills which filter out O 2 and plant cell material Obtain food and oxygen by using a muscular siphon that brings water to the gills which filter out O 2 and plant cell material Often attach themselves to surfaces Often attach themselves to surfaces Possess an open circulatory system Possess an open circulatory system GIANT CLAM

9. 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

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

11. Squid Caribbean Reef SquidTentacles of a giant squid Calamari: a deep fried squid dishSquid eye and gills

12. Octopus Octopus beak Octopus on the beach Swimming OctopusOctopus arm in detail

13. 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.

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

15. Squid Fact 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!