1. Chapter 9

2. Phylum Mollusca
One of the most successful groups of animals in the ocean
Have soft bodies, usually covered by a calcium carbonate shell
Wide range of sizes, lifestyles and relationships to humans (i.e., some are food, others cause commercial damage)

3. Phylum Mollusca
Mollusks are a large and varied group of animals that have a soft body and are most often covered with a calcium carbonate shell.
Their body is divided into two major parts (Figure 7.9).
The head-foot region includes the head, mouth, sensory organs and the foot, which is usually used for locomotion.

4. Phylum Mollusca
Their body is divided into two major parts (Figure 7.9).
The visceral mass includes all the other organ systems.
The mantle of mollusks covers the visceral mass and hangs from the sides of the body.
The mantle produces the shell and in some groups is used in locomotion or gas exchange. (Figure 7.10)

5. Phylum Mollusca
All mollusks except bivalves have a radula (Figure 7.10), a ribbon of tissue that contains teeth, used for scraping, tearing, piercing and cutting.

6. Molluscan Body 2 major parts:
head-foot: region containing the head with its mouth and sensory organs and the foot, which is the animal’s organ of locomotion
visceral mass: dorsal body region containing the other organ systems, including:
circulatory (heart and vessels)
digestive (stomach, digestive glands, intestine and anus)
respiratory (gill)
excretory reproductive systems

7. Figure 9-1 GENERALIZED MOLLUSCAN BODY PLAN.

8. Molluscan Body Mantle Radula
protective tissue covering soft parts, extends from the visceral mass and hangs down on each side of the body, secretes the shell
mantle cavity: space between the mantle and the body
Radula
a ribbon of tissue containing teeth (found in all except bivalves) used for scraping, piercing, tearing or cutting pieces of food

9. Figure 9-2 THE RADULA.

10. Class Polyplacophora Chitons
Have flattened bodies often covered by 8 shell plates.
Attach tightly to rocks, usually in intertidal zone.
Most scrape algae and other organisms off the rocks with radulae for food.

11. Figure 9-4 CHITONS.

12. Gastropod Molluscs
Gastropods move by sliding along the bottom on their foot.
Most gastropods have a shell, which may be coiled (e.g. snails) or not (e.g. limpets) (Figure 7.10).
Others, the nudibranchs, lack a shell.

13. Gastropod Molluscs
Many snails can retreat in their shell and close the aperture with the operculum (Figure 7.12), which can be used as defense or to reduce water loss in the intertidal zone.
The shape of the shell reflects the environment a snail is adapted to live in, for example; snails that live in exposed intertidal zones often have low, broad shells that reduce drag and allow them to cling to rocks.

14. Figure 9-6 GASTROPOD SHELLS.

15. Feeding and Nutrition
Gastropods have wide range of feeding strategies.
Herbivores usually eat small algae that they scrape off rocks with their radula. Some can eat seaweeds, such as kelp.
Carnivorous gastropods locate their prey with chemical cues, and eat a variety of prey including cnidarians, echinoderms and bivalves.

16. Feeding and Nutrition
Gastropods have wide range of feeding strategies.
Cone snails have a modified harpoon-like radula which is coated with a toxin and allows them to kill their prey.
Other gastropods are scavengers, deposit feeders (e.g. conch) or filter feeders (e.g. sea butterfly, Figure 7.13).

17. Figure 9-7 (a) GASTROPOD FEEDING STRATEGIES.

18. Nudibranchs Naked gastropods
Nudibranchs are marine gastropods that lack a shell (Figure 7.14).
They are often bright in color, which may be an indication of toxicity.
Many have cerata on their back, extensions of the mantle that increase the surface area of the mantle available for gas exchange.

19. Nudibranchs
Some nudibranchs will feed on cnidaria and retain their nematocysts as protection for themselves.

20. Figure 9-8 NUDIBRANCHS.

21. Bivalve Molluscs Class Bivalvia
Have shells divided into 2 jointed halves (valves)
Includes:
clams
oysters
mussels
scallops
shipworms

22. Bivalves
The body of bivalves is compressed laterally, and they have two valves (shells) attached dorsally by ligaments.
The valves are closed by adductor muscles and opened as the muscles relax and the weight of the valves pulls it apart.
Bivalves have no head or radula, and their foot is located ventrally and functions in burrowing and locomotion.

23. Bivalves
Their mantle forms inhalant and exhalent openings and cilia on the gills move water, exchange gases, and filter food particles that are then brought to the mouth (Figure 7.15)

24. Bivalve anatomy no head or radula laterally compressed bodies
shell halves attached dorsally at a hinge by ligaments
mantle often forms inhalant and exhalant openings to facilitate filter feeding
palps form the food into a mass for digestion and move it to the bivalve mouth

25. Figure 9-11 BIVALVE ANATOMY.

26. Bivalve Adaptations
Bivalves have evolved adaptations to live in a variety of different habitats.
Those that burrow in soft bottoms (infauna), such as clams, often have their mantle fused around their inhalant and exhalant openings, creating a siphon that can draw water in from above the sediment.

27. Bivalve Adaptations
Others live attached to the surface of hard substrates (epifauna), and may attach by cementing one valve to the substrate (e.g. oysters), or by byssus threads, made from a tough protein (e.g. mussels).
Unattached surface dwellers such as scallops and file clams can swim by jet propulsion as they open and close their valves rapidly.
Boring bivalves include some boring clams which live in soft rocks, and shipworms, which burrow into
wood by swallowing and digesting the wood, with the help of enzymes from their
symbiotic bacteria.

28. Bivalve Adaptations
Boring bivalves include some boring clams which live in soft rocks, and shipworms, which burrow into wood by swallowing and digesting the wood, with the help of enzymes from their symbiotic bacteria.

29. Cephalopod Molluscs Class Cephalopoda
Named after the foot, which is modified into a head-like structure
Ring of tentacles projects from the anterior edge of the head, for use in prey capture, defense, reproduction and sometimes locomotion
Except for nautiloids, they lack shells or have small internal shells

30. Types of cephalopods Nautiloid cephalopods
produce large, coiled shells composed of chambers separated by septa (partitions)
gas-filled chambers aid with buoyancy
siphuncle: cord of tissue connecting the nautiloid to uninhabited chambers (it inhabits the last chamber) which removes seawater from each chamber as it forms
head has tentacles coated with a sticky substance function in sensation or bringing food to the mouth

31. Figure 9-14 (b) SHELLED CEPHALOPODS.

32. nautiloids (continued)
move using jet propulsion
usually dwell on the bottom during the day and migrate to the surface at night
eat hermit crabs and scavenge for other food on the bottom
food is temporarily stored in a crop prior to transport to the stomach for digestion

33. Coleoid cephalopods (e.g. cuttlefish, squids, octopods)
cuttlefish have a bulky body, fins, 10 appendages (8 arms + 2 tentacles), and small internal shells
squids have:
large cylindrical bodies with a pair of fins derived from mantle tissue
10 appendages (8 arms + 2 tentacles) arranged in 5 pairs around the head and embellished with cup-shaped suckers which are attached by a short stalk and surrounded by toothed structures
the pen (a degenerate shell; an internal strip of hard protein) helps support the mantle

34. Figure 9-15 (b) CEPHALOPODS.

35. Figure 9-5 (c) CEPHALOPODS.

36. coleoids (continued)
octopods have 8 arms (no tentacles) with suckers without stalks or teeth, and sac-like bodies without fins
coleoids cloud water with a dark fluid called sepia containing melanin (a brown-black pigment) when disturbed
swim by jet propulsion by forcing water through a ventrally-located siphon or by fin undulation (in squids)
octopods – better adapted to crawling over bottom
have the most advanced, complex nervous system among invertebrates

37. Color and shape in cephalopods
arm/body movements and color changes are used in communication
chromatophores: special skin cells containing pigment granules which are concentrated or dispersed to change color
cephalopods can produce general body color changes or stripes and other patterns

38. Feeding and nutrition
carnivores – prey is located with highly developed eyes and captured by tentacles or arms
a pair of powerful, beak-like jaws in the oral cavity is used to bite or tear tissues; octopods use radula to drill holes in shells
diet depends on and varies with habitat
squids are pelagic: fish, crustaceans, squid
cuttlefish find invertebrates on the bottom
octopods forage or lie in wait near the entrances to their dens

39. Ecological Roles of Molluscs
Food for humans and other animals
snail shells are a calcium source for some marine birds
sperm whales consume masses of squid
Some snails are intermediate hosts to parasites
A few bivalves have commensal relationships (attaching to other animals)