1. Polyplacophora Gastropoda Bivalvia Scaphopoda Cephalopoda
Phylum Mollusca
Polyplacophora
Gastropoda
Bivalvia
Scaphopoda
Cephalopoda
Phylum Mollusca

2. Molluscs One of the largest of all phyla
Have adapted to a wide variety of habitats
Terrestrial, marine, benthic, and accomplished swimmers.
Phylum Mollusca

3. The Molluscan Body Plan
Despite the external differences between snails, clams, and squids the body plan is similar and distinct from all other phyla
The Mollusca body plan includes:
A large muscular foot
A radula
Mantle and mantle cavity
Usually a small head
Soft unsegmented body
A hard non-living calcareous shell
Phylum Mollusca

4. The Foot
Phylum Mollusca

5. The Radula
Radula
Phylum Mollusca

6. The Mantle The mantle is the body wall that enclose the body cavity
Phylum Mollusca

7. The Mantle Cavity Houses the visceral mass and comb-like gills
Gills are respiratory in function and can collect food particles
Mantle cavity also is the site for reproductive, excretory, and digestive systems
The molluscan coelom is very small; being restricted to the area surrounding the heart and gonads
Phylum Mollusca

8. Taxonomic Summary Phylum Mollusca Class Polyplacophora
Class Gastropoda
Class Bivalvia
Class Scaphopoda
Class Cephalopoda
Phylum Mollusca

9. Systems
Skeletal- Mantle may secretes a shell. Use hydrostatic pressure for ventral muscular foot.
Muscles -Ventral muscular foot and other muscles present.
Digestive- complete complex with salivary glands, digestive gland and Rasping tongue (Radula).

10. Systems
Circulatory - Open except for Cephalopoda. Dorsal heart, usually in a pericardial cavity.
Respiratory - Ctenidia (gills) in mantle cavity, respiratory pigment is copper.
Phylum Mollusca

11. Systems
Excretory- by nephridia usually connecting to the pericardial cavity,
the coelom is usually reduced to the cavities of the nephridia, gonads and pericardium.
Nervous - Nerve ring with various pairs of ganglia—two pairs of nerve cords, one innervating the foot, the other the visceral mass (modified ventral ladder-like system)

12. Systems Integumentary – Mantle
Endocrine - nervous systems produces hormones.
Reproductive - varied- monoecious, protandric, or dioecious. Larva in marine = trochophore and veliger, in freshwater clam is glochidium.
Phylum Mollusca

13. Phylum Mollusca
Class Polyplacophora
Phylum Mollusca

14. Class Polyplacophora
Chitons
Phylum Mollusca

15. Chiton Lifestyles
Found close to shore mainly in the intertidal where they live on hard substrates
Strong foot and low profile help from being swept away
Phylum Mollusca

16. Ingestion and Digestion
Radula is used to scrape algae from the rocks
Mouth is anterior and anus is posterior; linear digestive tract
Phylum Mollusca

17. Phylum Mollusca
Class Gastropoda
Phylum Mollusca

18. Class Gastropoda Defining characteristics
Visceral mass and nervous system become twisted ° during embryonic development
Largest and most varied group of the phylum Mollusca
Phylum Mollusca

19. Gastropod Morphology and Movement
The typical snail consists of a visceral mass, which sits atop a muscular foot
The visceral mass is protected by a univalve shell that is coiled
Phylum Mollusca

20. Phylum Mollusca

21. Prosobranchia Anatomy
Molluscan gill
Consists of a series of flattened, triangular sheets
Water is drawn into the animal by gill cilia
Phylum Mollusca

22. Phylum Mollusca
Class Bivalvia
Phylum Mollusca

23. Class Bivalvia Defining characteristics
Two-valved shell
Body flattened laterally
This class contains clams, oysters, mussels, scallops, and shipworms
Phylum Mollusca

24. Bivalves and You Many species are edible
In today’s waters this can cause certain problems since bivalves are filter feeders
Also, an important food item for our commercially important fish
Important to humans in their ability to strain harmful bacteria out of polluted waters
Some can pump up to 40 liters per hour
Phylum Mollusca

25. Bivalve Locomotion?
Most bivalves move by expansions and contractions of the foot
Mussels usually are sessile and attach to substrate with threads
Phylum Mollusca

26. Phylum Mollusca

27. Bivalve shells
Protein hinge ligament stores energy required to open the shell
Adductor muscles is responsible for closing the valves
The umbo is dorsal and the valves are addressed as left and right
Siphons are posterior and the excurrent siphons are always dorsal
Phylum Mollusca

28. Phylum Mollusca

29. The Mantle
Phylum Mollusca

30. Bivalve Feeding Bivalves are filter feeders
Ctenidia, gills, are used for feeding & respiration and are enlarged and folded to increase surface area
Cilia on the gills create a current to bring food-laden water into the mantle cavity
Phylum Mollusca

31. Bivalve Reproduction Dioecious
The male sheds sperm into the water column
Sperm can enter the female or fertilization can occur in the water column
Phylum Mollusca

32. Class Scaphopoda Class Cephalopoda
Phylum Mollusca
Class Scaphopoda
Class Cephalopoda
Phylum Mollusca

33. Class Scaphopoda Defining characteristics
Tusk shaped conical shells, open at both ends
Development of anterior thread-like adhesive feeding tentacles
Elongated tapering tubular shells that burrow in sandy bottoms
Phylum Mollusca

34. Phylum Mollusca
Class Cephalopoda
Phylum Mollusca

35. Class Cephalopoda Defining characteristics Closed circulatory system
Foot modified to form flexible arms and siphons
Ganglia fused to form a large brain encased in a cartilaginous cranium
Phylum Mollusca

36. Cephalopod Characteristics
The most highly organized of all the molluscs, the foot is closely associated with the head
Nautilus, octopus, cuttlefish, and squids
Shell size varies from a full shell (nautilus) to a vestige of a shell in the squid and octopus
Can be as large as 1,000kg. and 18m.
Phylum Mollusca

37. Squids Octopuses Chambered Nautiluses 10 tentacles.
Propels by pumping jets of water with the mantle through an excurrent siphon.
Octopuses
8 tentacles
They often crawl along the ocean bottom or lie in wait for prey.
Chambered Nautiluses
The only existing cephalopod with external shell.
Shell is coiled & divided into chambers.
The body is confined to the outermost chamber.

38. Defensive Mechanisms
Since they are susceptible to predation they have evolved chromatophores
May posses hundreds or thousands, all controlled by the brain
An ink sac that is associated with the digestive system and discharged out the anus
Phylum Mollusca

39. Sensory & Nervous System
Eyes
All but the nautilus have image forming eyes that are like mammals
Convergent evolution
Phylum Mollusca

40. Reproduction Sexes are separate
Males have one modified arm (hectocotylus) for sperm transfer
Sperm are enclosed in packets called spermatophores
Phylum Mollusca

41. Squid 10 sucker bearing arms surround the mouth
2 longer tentacular arms can shoot forward and capture prey
Large bites of food are removed and swallowed quickly
Form large schools and feed on crustaceans, and fishes
The shell is reduced and lies under the mantle, pen
Large folded gills and a circulatory system distribute oxygen quickly
High oxygen demands are meet by the contraction of the mantle cavity
This method also removes waste products
Phylum Mollusca

42. Squid Internal Anatomy
Phylum Mollusca

43. Squid Locomotion The foot forms the funnel
The upper end of the mantle is extended into a pair of triangular fins
Water enters the mantle cavity at the free end
When the mantle contracts the edge is tightly sealed and water is forced out the funnel
Can move very quickly
5-10 m/s
Phylum Mollusca

44. Octopods Have 8 arms all equal in length
Rows of suckers from base to tip
Compact body with a greatly reduced shell
The body is extremely flexible and assumes a streamlined shape when swimming with squid-like jets through the funnel
Phylum Mollusca

45. Learning and Memory Benthic feeders on bivalves, crabs and fishes
Some are pelagic and spend their entire life swimming, usually at great depths
Amazing ability to learn quickly and remember for several weeks
Phylum Mollusca