1. Molluscs and Annelids (Mollusks)

2. PHYLUM MOLLUSCA
THE MOLLUSCS 2

3. What is a mollusk? Basic answer:
Slugs, snails, and animals that once lived in shells in the ocean or on the beach are all mollusks.

4. INTRODUCTION
Mollusca means “soft.” Most molluscs have shells for protection
Eight diverse classes of molluscs with more than 100,000 named species
Includes snails, clams, squids, octopuses, nautiluses, etc
Found in almost all habitats. The need for calcium is a major limiting factor

5. Characteristics of Mollusk:
An advanced nervous system
Many types of feeders, including, carnivores, herbivores, filter-feeders and grazers. All but one class have a radula, a ribbon-like structure with teeth of chitin that scrapes, cuts or tears food
Most molluscs are dioecious. They have a free-swimming trochophore larva; many also have a veliger larva stage

6. CHARACTERISTICS, Cont. An advanced nervous system
Many types of feeders, including, carnivores, herbivores, filter-feeders and grazers. All but one class have a radula, a ribbon-like structure with teeth of chitin that scrapes, cuts or tears food
Most molluscs are dioecious. They have a free-swimming trochophore larva; many also have a veliger larva stage

7. CHARACTERISTICS, Cont. Durable shells
found in marine, freshwater, and terrestrial habitats
One of the most successful of all phyla – only arthopods have more terrestrial species
Important food source for humans
Coelom – very important
2 body opeings

8. Not entirely beneficial
Economic importance
– pearls mother –of –pearl jewelry and other jewelry
Food source
Not entirely beneficial
- shipworms – destructive to timber submerged in sea
slugs, terrestrial snails can cause extensive damage to flowers, gardens an crops
hosts to intermediate stages for many serious diseases

9. Body size

10. External body plan Some mollusks have shells
Some are adapted to live without a hard covering (slugs and squids)
Bivalve – 2 shelled mollusks (clams oysters, scallops)

11. External body plan - bivalve
Umbo
Growth lines
Ventral side –
Dorsal side

12. UMBO tells direction
Anterior
Posterior
Dorsal
Ventral

13. NO CEPHALIZATION (No head)
Shell = valve (Bivalves = 2 shells)
Growth rings
Adults = sessile (stay in one place)

14. Internal body plan - bivalve
Siphon
Exhalent
Inhalent
Adductor muscle
Distinct bilateral symmetry
Visceral mass
Muscular foot
Mantle
gills

15. THE MOLLUSCS 15

16. VISCERAL MASS
Contains heart, digestive, excretory, reproductive

18. INCURRENT & EXCURRENT SIPHONS
move food
up toward
mouth
CILIA on gills pull in water

19. Describe the function of gills

20. GILLS Trap food (PALPS move it forward) Ridges for more surface area
(like typholosole)
Gas exchange
Diffusion moves oxygen & carbon dioxide across membrane

21. Mollusc shell Secreted by mantle
Protects the 2 underlying layers form erosion
Pearls

22. THE MOLLUSCS 22

23. Describe the different functions of the mantle
( include the role of the continuous stream of water)
Some molluscs can withdraw into mantle davity for protection
In aquatic molluscs a continuous stream of water is passed into and out of this cavity by the cilia on the gills
This action brings in oxygen and in the case of bivalves food
Carries out waste material
In squids and octopuses the mantle cavity has been modified to create the jet propulsion system that enables these animals to move rapidly through the water.

24. ADDUCTOR MUSCLES
Turn POSTERIOR END toward door Cut your adductor muscles to open shell

25. Functions of the foot

26. Describe how molluscs obtain food

27. Circulatory system in molluscs
Open system of circulation
Closed circulatory system
heart

28. OPEN CIRCULATION Blood flows loose inside coelom and tissue spaces
Reduced Coelom = pericardial cavity
(space around heart)

29. Excretion in molluscs
REFER TO PREVIOUS DIAGRAM

30. Respiration in molluscs

31. NERVOUS SYSTEM 2 pairs of nerve cords 3 pairs of ganglia
3 pairs of ganglia
2 pairs of nerve cords

32. Reproduction in Molluscs
TROCHOPHORE LARVA
VELIGER LARVA
BACK
THE MOLLUSCS 32

33. CLASSIFICATION Of the 8 mollusc classes, we’ll look at 3:
Class Polyplacophora- the chitons
Class Scaphopoda- the tooth shells
Class Gastropoda- the snails
Class Bivalvia- the clams, oysters
Class Cephalopoda- octopuses, squids

34. Three main classes of molluscs

35. Gastropoda

36. CLASS GASTROPODA
The snails, slugs, whelks, limpets, conchs, periwinkles and others
Largest, most diverse group of molluscs
One-piece shell, usually coiled
Mostly herbivores; radula for feeding
Land and freshwater gastropods have lungs

37. THE MOLLUSCS 37

38. THE MOLLUSCS 38

39. SEA SLUG: CLASS GASTROPODA
THE MOLLUSCS 39
SEA SLUG: CLASS GASTROPODA

40. Bivalvia

41. CLASS BIVALVIA Have 2 shells
Includes clams, oysters, scallops and mussels
Sedentary filter-feeders. The only molluscan group with no radula

42. THE MOLLUSCS 42
A GIANT CLAM

43. THE MOLLUSCS 43

44. Cephalopoda

45. CLASS CEPHALOPODA The squids, octopuses and nautiluses
Among the most advanced of all invertebrates
Active predators living in the ocean, which requires them to be fast, smart, coordinated and possess good eyesight
They have a funnel-like structure allowing for movement by jet propulsion
Arms and/or tentacles for grasping. The tentacles have suckers

46. CEPHALOPOD SHELLS
Only the members of the genus Nautilus possess an external shell. Unlike the shells of gastropods nautiloid shells are divided by septa into a series of chambers. The animal lives only in the outer chamber
Cuttlefish have an internal chambered shell
Squids have a small internal sheet-like shell
Octopuses have no shell

47. CEPHALOPOD EYESIGHT
Nautiloids have relatively poor eyesight compared to other cephalopods
Other cephalopods have image-forming eyes similar to mammals, but they evolved separately (convergent evolution). Cephalopod eyes possess structures similar to mammalian eyes, but they focus differently

48. THE MOLLUSCS 48

49. SQUID
THE MOLLUSCS 49

50. THE MOLLUSCS 50
AN OCTOPUS

51. OCTOPUS
THE MOLLUSCS 51

52. THE MOLLUSCS 52
Nautilus Anatomy

53. Nautilus
BACK
THE MOLLUSCS 53

54. Reproduction in Cephalopods
Sexes are separate
Sperms stored in spermatophores – a sac that opens into mantle cavity
Male uses a tentacle to transmit spermatophore from cavity into female cavity
Female fertilizes eggs as they leave the oviduct
Attach to stones or other objects