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Chapter 12 Molluscs. 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. Characteristics of Phylum Mollusca. Wide variety of habitats

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Chapter 12 Molluscs


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    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

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

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

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

    9. 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

    10. Mollusk Body Plan

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

    12. 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

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

    14. 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

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

    16. Video clip- aquatic snail (note heart)

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

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

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

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

    21. 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

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

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

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

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

    26. 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

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

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

    29. 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)

    30. Land snail • Food for humans

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

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

    33. Slug • No shell • Garden pest

    34. Limpets • Cling to rocks or other surfaces

    35. Conch • Large shell • Marine • herbivores Human impact Feeding on ocean floor

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

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

    38. Bivalve shell morphology Umbo- oldest part of shell • Growth in concentric lines around it

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

    40. Water movement through bivalves • incurrent siphon - water into the mantle cavity • water circulates over the gills • Gas exchange • Filter feeding

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

    42. 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

    43. 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

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

    45. Zebra mussel • Environmental Pest • Ballast water of ships from Europe in 1986 Zebra mussel

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

    47. Zebra Mussels (cont’d) • Live in high densities • Reproduce rapidly Lake Michigan http://epod.usra.edu/archive/epodviewer.php3?oid=135264

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