Chapter 12 Molluscs

1. Chapter 12Molluscs

2. octopus snail clam slug chiton scallop cuttlefish Nautilus Giant squid Architeuthis Phylum Mollusca • molluscus= “soft body” • ~ 100,000 species • diverse • Size: < 1 cm  18 m long

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

4. (Endoderm) (mesoderm) 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)

5. Fig. 9-13, p188

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

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

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

11. Snail radula Head-foot 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. Octopus http://acolyte.org/images/octopus.png Head-foot Foot: • ventral • Muscular structure • Locomotion • Attachment • modifications

14. Chiton 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

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. Video clip- aquatic snail (note heart)

19. Long-finned squid-Loligo http://www.biology.ualberta.ca/courses.hp/zool250/Labs/Lab08/Lab08.htm Molluscan reproduction • Mostly dioecious Giant squid

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

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

22. http://www.ucmp.berkeley.edu/mollusca/scaphs/scaphopoda.html Class Scaphopoda • Tooth shells • Long, slender body • Burrows into mud • Shell open at both ends

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

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 http://eebweb.arizona.edu/collections/Fishes/Photographs.htm Red abalone Moon snail- uses radula to drill holes in bivalve (ie. clams)

32. Land snail • Food for humans

33. Cone snail Barbed radula tooth containing neurotoxin- powerful analgesic Cone snail • 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 • herbivores Human impact Feeding on ocean floor

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

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

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

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. http://www.csc.noaa.gov/scoysters/images/bio/oysters2.jpg Oyster • lower valve is cemented to any object available • Improve water quality • Decrease bank erosion • food

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

47. Zebra mussel • Environmental Pest • Ballast water of ships from Europe in 1986 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 Lake Michigan http://epod.usra.edu/archive/epodviewer.php3?oid=135264

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