Class Gastropoda

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 groups: • Caenogastropoda: includes gilled snails • Opisthobranchs - reduced shell • Pulmonata - lungs

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

9. Caenogastropoda • A. slit shells - deep water species • Abalones (Haliotis) • 9 spp on our Pacific coast • Commercially harvested

10. Caenogastropoda • B. keyhole limpets - Fissurella • conical shells • C. Limpets - Acmaea

11. Caenogastropoda • D. topshells, turban shells, star shells • Astraea

12. Neritimorpha • E. Nerites (Nerita) intertidal in Caribbean • some freshwater + terrestrial

13. Prosobranchs • Male with penis • Fertilization internal • 1 monopectinate gill • 1 auricle • 1 coeloduct

14. Prosobranchs • A. Freshwater apple snails - • Viviparus, Pomacea

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

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

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

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

19. 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

20. Cowries

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

22. H. Moon shells - predators on molluscs: • bore into shells • Lunatia • Polinices

23. 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

24. I. Helmet shells, tritons, tuns • Predators on molluscs and echinoderms • Long proboscis • Large shells

25. J. Periwinkles - intertidal • Littorina

26. Mostly same characteristics as Mesogastropoda • Radula has only 3 teeth in a transverse row • Most are marine • Most are carnivores

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

28. B. Whelks - Busycon • Tulip shells - Fasciolaria • Predators and carrion feeders

29. C. Olives, miters, and volutes • Colorful, mostly tropical snails • prey on invertebrates

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

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

32. “Glory of the sea” cone shell

33. 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

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

35. 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

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

37. 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

38. More Pteropods

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

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

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

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

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

44. 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

45. 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)

46. Foot

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

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