1. Chapter 12 Molluscs

2. Phylum Mollusca ~ 100,000 species diverse Size: < 1 cm  18 m long
octopus
Phylum Mollusca
molluscus= “soft body”
~ 100,000 species
diverse
Size: < 1 cm  18 m long
snail
Giant squid Architeuthis
slug
scallop
chiton
Chittons, Gastropods, bivalves, cephalopods
Chitons Tooth shells, Snails, Slugs, Nubibranchs, Sea butterflies, Clams, Mussels, Oysters, Squid, Octupus, Nautilus
Giant squid Architeuthis = 18 m long, 1000 lbs
Giant clam (Tridacna gigas) = 1.5m long, 500lbs
Nautilus
cuttlefish
clam

3. Characteristics of Phylum Mollusca
Wide variety of habitats
Tropics  polar seas
Most are marine, some freshwater, some terrestrial
Giant clam

4. Characteristics of Phylum Mollusca
Eucoelomates
True coelom, lined with mesodermal peritoneum (membrane that lines coelom, covers coelomic viscera)
mesentery- mesodermal sheet that suspends internal organs in coelom
Schizocoelous
Coelom forms by splitting of mesodermal bands (next slide)
(Endoderm)
(mesoderm)

5. In enterocoelous formations, the ceolom comes from pouches of the primitive gut (archenteron)
Fig. 9-13, p188

6. Architectural patterns of animals
Architectural patterns of animals. These basic body plans have been variously modivied during evolutoinary descent to fit aimals to a great variety of habitats. Ectoderm is shown in gray, mesoderm in red, and endoderm in yellow

8. Characteristics of Phylum Mollusca
Unsegmented
closest common ancestor shared with segmented worms (Phylum Annelida) (ie. earthworms)

9. Characteristics of Phylum Mollusca
All organ systems are present, well-developed
Respiratory organs
Circulatory system, with heart
Greater body size possible
Freshwater clam
Squid

10. Molluscan body form
2-part body plan:
Head-foot
Visceral mass
Octopus

11. Head-foot Head: anterior Cephalic sensory organs Feeding organs:
Snail radula
Head:
anterior
Cephalic sensory organs
Feeding organs:
Radula
Most molluscs (not bivalves)
rasping structure
Tongue-like
Rows backward-pointing “teeth”
Scraping food
drilling

12. Mollusk Body Plan

13. Head-foot Foot: ventral Muscular structure Locomotion Attachment
modifications
Octopus

14. Visceral mass Digestive organs Reproductive organs Circulatory organs
Respiratory organs
Mantle
Attached to visceral mass
Dorsal skin folds
protective
In some, mantle secretes protective shell over visceral mass
Chiton

15. Mantle cavity Space between mantle and foot Opens to outside
Functions:
Gas exchange (respiration)
Excretion/elimination
Release reproductive products

16. Circulatory system of molluscs
Open circulatory system (except Class Cephalopoda)
Open circulatory system
heart pumps hemolymph (blood) through body cavity, b/w cells
No small blood vessels

17. Circulatory system of molluscs
Closed circulatory system (Class Cephalopoda)=
Blood confined to vessels

18. Movie- aquatic snail (note heart)

19. Molluscan reproduction
Mostly dioecious
Giant squid
Long-finned squid- Loligo

20. Classes of Molluscs Class Polyplacophora Class Scaphopoda
Class Gastropoda
Class Bivalvia
Class Cephalopoda
Others…

21. Classes of Mollusc Class Polyplacophora “many plate-bearers” Chitons
Dorsoventrally flattened
Shell= 8 overlapping dorsal plates
marine
Underside of chiton

22. Class Scaphopoda Tooth shells Long, slender body Burrows into mud
Shell open at both ends

23. Class Gastropoda Gastro= gut Poda= foot
Limpet
Gastro= gut
Poda= foot
Snails, limpets, slugs, whelks, conchs, periwinkles, abalone, sea slugs….
Largest class
Most diverse
Marine, freshwater, terrestrial
Silver cloud nudibranch
Pulmonate snail
Images:

24. Class Gastropoda (cont’d)
Microscopic  1m long (sea hare)
Typically 1-8cm long

25. Class Gastropoda (cont’d)
Basically bilateral
Visceral mass, mantle, mantle cavity undergoes torsion (twisting) asymmetrical

26. Class Gastropoda (cont’d)
Moves mantle cavity, w. gills, anus, visceral organs to anterior

27. Class Gastropoda (cont’d)
Why torsion?
Head withdraws into shell first
Clean, undisturbed H2O enters mantle cavity

28. Coiling Absent in some Visceral mass/mantle may be coiled
Successive coils- whorls
Caused pressure on right side  adaptation: loss of rt. kidney, auricle, gill
Water enters via left, leaves right

29. Class Gastropoda (cont’d)
May have protective shell

30. Class Gastropoda Well-developed sense organs
Eyes at base or at end of tentacles

31. Gastropod feeding habits:
Herbivores
Carnivores
Red abalone
Moon snail- uses radula to drill holes in bivalve (ie. clams)

32. Land snail
Food for humans

33. Barbed radula tooth containing neurotoxin- powerful analgesic
Cone snail
Cone snail
Barbed radula tooth containing neurotoxin- powerful analgesic
Marine
Venomous
Contain analgesic
Video Eating fish
Nat Geo Cone snail

34. Abalone
Several holes in top of shell
Excrete waste
Food for humans

35. Slug
No shell
Garden pest

36. Limpets
Cling to rocks or other surfaces

37. Conch Large shell Marine Many are predators Human impact
Feeding on ocean floor

38. Class Bivalvia clams, oysters, mussels, scallops
soft body between two halves of a hinged shell
Giant clam
California mussel

39. Class Bivalvia (cont’d)
Aquatic
most marine, some fresh water
no tentacles, head, radula
adductor muscle
Large cilia-covered gills (in most)

40. Bivalve shell morphology
Umbo- oldest part of shell
Growth in concentric lines around it
Pallial line- line of mantle attachment

41. Valves open by adductor muscle
contraction= closed
relaxing= open
Hinge= mantle secretion of more protein, less calcium carbonate

42. Water movement through bivalves
incurrent siphon - water into the mantle cavity
water circulates over the gills
Gas exchange
Filter feeding
organic matter sticks to mucous on surface of gills
iv. cilia on surface of gills (gill rakers) carry particles to the mouth “mucous feeder” - “filter feeder”

43. Water movement through bivalves (cont’d)
water flows past anus where waste is excreted
excurrent siphon – water out of the mantle cavity

44. Locomotion Mostly sedentary/sessile highly developed muscular foot
often to burrow into sediment
move by slicing-like motion of foot
swim by chattering motion of shell (scallops)
Clams not just for chowder movie

45. Oyster lower valve is cemented to any object available
lower valve is cemented to any object available
Improve water quality
Decrease bank erosion
food

46. Pearl Production protective function
foreign substance between mantle & shell
mantle secretes pearly layers of nacre around substance
Developing pearl
Epithelium
Shell

47. Zebra mussel Environmental Pest
Ballast water of ships from Europe in 1986
The zebra mussel (Dreissena polymorpha) has become a bane to the Great Lakes and is a multibillion dollar problem affecting industrial and public water supplies. They're nonindigenous invaders originally found in Eastern Europe, around the Black and Caspian Seas. In 1988, they were inadvertently introduced to the Great Lakes in the ballast water of a transatlantic freighter and, in less than 10 years, they've spread to all five Great Lakes and have now found their way into a number of major rivers. A female can release up to one million eggs each season, so accidentally transporting just one zebra mussel can lead to big problems in waterways where they've yet to appear. These fresh water mollusks look like small clams and they're usually a yellowish-brown color with dark and light colored stripes. Most zebra mussels are smaller than an inch (2.54 cm) in length, but they can be up to two inches (5.1 cm) long. They're most often found in dense clusters and prefer shallow (6-30 feet or 2-10 m), algae-rich water. Densities of over 1 million per square meter have been recorded in parts of Lake Erie! Adult zebra mussels colonize all types of living and non-living surfaces including boats, power plants, water-intake pipes, docks, and slow moving animals such as native clams and turtles. They even attach to each other. When they attach to clams, as shown above, they prevent these bivalves from opening. The survival of several clam species and a variety of North American ecosystems are threatened by the spread of these alien invaders.
More information:
Zebra mussel

48. Zebra Mussels (cont’d)
attach to any hard substrate
Other mussels, clams, crayfish water pipes, docks, boats
Outcompete other bivalves

49. Zebra Mussels (cont’d)
Live in high densities
Reproduce rapidly
This photo shows zebra mussel shells (Dreissena polymorpha) littering the Lake Michigan shore at Point Beach State Forest, Two Rivers, Wisconsin. These invaders from the Caspian Sea region have caused billions of dollars in damage to industry, agriculture and fresh water supplies. They were first discovered in 1988 and believed to have been dumped from ballast tanks of oceanic vessels into Lake St. Clair. They're populating lakes farther inland by attaching themselves to recreational boats. Latest findings indicate that these inch-long (2.54 cm) creatures may be a threat to the food chain of Lake Michigan's whitefish as well as other species. Their numbers in the Great Lakes and virtually every connecting body of water in the Great Lakes watershed is out of control. Adult zebra mussels colonize nearly all types of living and non-living surfaces including boats, water-intake pipes, docks, slow moving animals such as clams, even each other. See also the Earth Science Picture of the Day for May 16, 2002.
Lake Michigan

50. Zebra Mussels (cont’d)
Killed all native mussels in Lake Erie

51. Distribution of Zebra Mussel

52. Giant Clam & Burrowing Clam
some= food
Siphon
Burrowing clam
Giant clam

53. Scallops
coarsely ribbed
food

54. Shipworms
Destructive
Burrow into wood

55. Class Cephalopoda squid, octopus, nautilus, cuttlefish ammonoids
“head foot”
Largest, most complex invertebrates

56. most highly developed mollusc Marine predator
Most active and intelligent
Marine predator
carnivorous
Cuttlefish camouflage
Cuttlefish

57. shell reduced/absent & internalized (vestigal) (squid, octopus)
Nautilus- shell
Cuttlefish- small, enclosed by mantle
Octopus
Vestigal- rudimentary organ that was once well-developed in ancestor but is now degenerate

58. head is well developed - large eyes
Complex eyes (except Nautilus)
Cornea, lens, chambers, retina, iris
Well-developed nervous system - complex brain
Squid

59. foot is modified into multiple tentacles with suckers (in some)
Grasp prey
Taste via suckers
crawling
Movie MBA
siphon forces out water: “jet propulsion”
Octopus movement movie, octopus movement, MBA MBA

60. squid & octopus possess ink gland which produce melanin ; escape

61. Octopus Eight arms with suckers Crawl or eject water from siphon
Change skin color
Most intelligent invertebrate
Colorblind, but can be taught different shapes

62. Octopus
camouflage

63. Some octopi can kill humans:
Blue-ringed octopus
Size of golf ball
Bacteria in salivary glands
Paralysis, but victim fully conscious
Blue-ringed octopus
The Southern Blue Ringed Octopus (Hapalochlaena maculosa) occurs in Southern Australia and is recognised by small blue rings that cover the upper body and the arms. The Greater Blue Ringed Octopus (h.lunulata) has larder rings and occurs in Northern Australia and farther north in the tropic western Pacific Ocean. Other species are recognised by different patterns of blue on the body. The Blue-Lined Octopus (H. fasciata) from New South Wales has blue lines instead of rings on the body, but blue rings on the arms. Blue-ringed octopus are thought to harness bacteria in their salivary glands to produce tetrodotoxin found in poisonous puffer fishes. Several human fatalities have been attributed to bites from these small octopuses.
The powerful venom acts on the victim's voluntary muscles, paralysing the muscles required for body movement and breathing. Mouth to mouth resuscitation can keep the victim alive and the poison gradually wears off after 24 hrs, apparently leaving no side effects. Such patients that have survived such an experience talk of the terror of lying immobile and conscious while people around them are convinced of their demise.

64. Nautilus Up to 94 tentacles Shell with many gas chambers No suckers

65. Ammonoids
Extinct
400 to 65 MYA
Died out with dinosaurs