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Class Gastropoda

Class Gastropoda. Snails - largest class of molluscs ~ 85,000 living spp. ~ 15,000 fossil spp. Habitats: marine benthos, ocean plankton, freshwater, land. After torsion. Gastropod characteristics. 1. Torsion - primitive bilateral symmetry lost during development

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Class Gastropoda

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  1. Class Gastropoda • Snails - largest class of molluscs • ~ 85,000 living spp. • ~ 15,000 fossil spp. • Habitats: marine benthos, ocean plankton, freshwater, land

  2. After torsion Gastropod characteristics • 1. Torsion - primitive bilateral symmetry lost during development • Twisting of visceral mass, mantle, and mantle cavity

  3. Gastropod characteristics • 2. Definite head: eyes, tentacles • 3. Flat ventral foot • 4. Mantle cavity w/gills or lungs • 5. Buccal cavity w/ radula

  4. plano-spiral helico-spiral Characters cont. • 6. Coiled shell - one continuous piece • operculum on posterior foot of some

  5. Characters, cont. • 7. Centralized complex nervous system • 8. Hermaphroditic or dioecious • 9. Oviparous or ovoviparous

  6. 10. Larval form • Archaeogastropoda have trochophore larva • Many marine snails have veliger larva • Freshwater + terrestrial species usually hatch as young snails

  7. Gastropod classification • 3 subclasses: • Prosobranchia • Opisthobranchi - reduced shell • Pulmonata - lungs

  8. Subclass Prosobranchia • Mantle cavity anterior • 1 or 2 gills • shell and operculum usually present • most are dioecious

  9. Prosobranchs, Order Archaeogastropoda • Primitive snails • External fertilization • Trochophore larva • 2 bipectinate gills • 2 auricles • 2 coelomoducts

  10. Prosobranchs, Order Archaeogastropoda • A. slit shells - deep water species • Abalones (Haliotis) • 9 spp on our Pacific coast • Commercially harvested

  11. Prosobranchs, Order Archaeogastropoda • B. keyhole limpets - Fissurella • conical shells • C. Limpets - Acmaea

  12. Prosobranchs, Order Archaeogastropoda • D. topshells, turban shells, star shells • Astraea

  13. Prosobranchs, Order Archaeogastropoda • E. Nerites (Nerita) intertidal in Caribbean • some freshwater + terrestrial

  14. Prosobranchs, Order Mesogastropoda • Male with penis • Fertilization internal • 1 monopectinate gill • 1 auricle • 1 coeloduct

  15. Prosobranchs, Order Mesogastropoda • A. Freshwater apple snails - • Viviparus, Pomacea

  16. Prosobranchs, Order Mesogastropoda • B. Turret shells - worm shells; caecums, ceriths, some freshwater genera, all have high shells

  17. Prosobranchs, Order Mesogastropoda • C. Violet snails - pelagic grazers on man o’war • Vellela, Porpita • Janthina: secretes bubble mass for floatation

  18. Prosobranchs, Order Mesogastropoda • D. Cap shells, slipper shells • Crepidula change sex w/age • see slides of veliger larva

  19. Prosobranchs, Order Mesogastropoda • E. Conchs - Strombus • Feed on algae, turtlegrass • Commercial harvest in Caribbean

  20. Prosobranchs, Order Mesogastropoda • F. Cowries; Cypraea - graze on algae, sponges, gorgonians, and tunicates • Mantle covers most of shell when extended • Favorites of shell-collectors • No periostracum • Italians call them “porcellanos” = little pigs • Porcelain got its name

  21. Cowries

  22. Prosobranchs, Order Mesogastropoda • G. Heteropods - pelagic, swimming snails w/reduced shell • Carinaria (see Fig. 10-30, p. 399)

  23. Prosobranchs, Order Mesogastropoda • H. Moon shells - predators on molluscs: • bore into shells • Lunatia • Polinices

  24. Moon shells: • Muscular suction disk holds snail on clam shell • Drill through shell with radula: • Wiggle proboscis into flesh • Remove most of flesh from clam

  25. Prosobranchs, Order Mesogastropoda • I. Helmet shells, tritons, tuns • Predators on molluscs and echinoderms • Long proboscis • Large shells

  26. Prosobranchs, Order Mesogastropoda • J. Periwinkles - intertidal • Littorina

  27. Prosobranchs, Order Neogastropoda • Mostly same characteristics as Mesogastropoda • Radula has only 3 teeth in a transverse row • Most are marine • Most are carnivores

  28. Prosobranchs, Order Neogastropoda • A. Drills - Murex, Urosalpinx • Drill holes in shells of bivalves and barnacles • Oyster drill and others cause economic losses

  29. Prosobranchs, Order Neogastropoda • B. Whelks - Busycon • Tulip shells - Fasciolaria • Predators and carrion feeders

  30. Prosobranchs, Order Neogastropoda • C. Olives, miters, and volutes • Colorful, mostly tropical snails • prey on invertebrates

  31. Prosobranchs, Order Neogastropoda • D. Cones - Conus • Most prey on inverts • Those that prey on fish can be dangerous to humans • Fig 10-42, p. 409

  32. Conus • Long proboscis with harpoon-like radular tooth • venom gland

  33. “Glory of the sea” cone shell

  34. Subclass Opisthobranchia • Detorsion - brings mantle cavity to right side • 1 gill, 1 auricle, 1 coelomoduct • Shell often reduced or absent • Mantle cavity often reduced or absent • Many are secondarily bilateral symmetric • Hermaphroditic

  35. Subclass Opisthobranchia • A. Bubble shells - Bulla • Predators with thin, reduced shell

  36. Subclass Opisthobranchia • B. Sea hares - Aplysia • Thin, caplike shell overgrown by mantle • Vegetarians (herbivores) • Can eject milky fluid from mantle cavity • A. californica has largest body of all gastropods

  37. Subclass Opisthobranchia • C. Sea slugs • With or w/o shell • Berthelinia is a “bivalve” gastropod • Fig. 10-23, p. 392

  38. Subclass Opisthobranchia • D. Pteropods or sea butterflies • 2 orders with and w/o (naked) shells • Planktonic with foot modified into wing-like flaps for swimming • Often occur in enormous numbers

  39. More Pteropods

  40. Subclass Opisthobranchia • E. Nudibranchs • Often with secondary gills and cerata (hornlike dorsal projections) • Many endemics

  41. Subclass Opisthobranchia • F. Parasitic Opisthobranchs • 2 orders • One ectoparisitic on bivalves and annelids • One endoparasitic in sea cucumbers

  42. Subclass Pulmonata • Charactistics like Opisthobranchia, but w/o gill • Mantle cavity converted to lung • Shell usually present • No operculum • Hermaphroditic

  43. Subclass Pulmonata • A. freshwater snails: • Lymnaea, Physa, Planorbis • Freshwater limpets • Most come to surface for air • Some have developed secondary gills • Descended from terrestrial ancestors

  44. Subclass Pulmonata • B. Land snails and slugs • Helix • Limax • C. Intertidal slugs w/posterior anus

  45. Class Scaphopodatusk shells • ~ 300 spp. • Sedentary, marine burrowing, in 6 - 1800 m depth • Shells resemble elephant tusks • Most burrow in sand, few in mud • Feed on microscopic organisms; foraminiferans • Considered offshoot of early bivalve ancestors

  46. Scaphopod characteristics • 1. Tusk-like shell open at both ends • 2. Bilateral symmetry (like bivalves) • 3. Rudimentary head • no eyes • Head has threadlike, food gathering tentacles (captacula)

  47. Foot

  48. Scaphopod characteristics • 4. Radula present • 5. Circulatory system reduced - sinuses • Gills absent • 6. Dioecious, trochophore and veliger larval stages

  49. Scaphopod classification • Two families (representative species): • Dentalium - conical shell • Cadulus + Siphonodentalium - globular shell, enlarged foot

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