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Class Gastropoda.ppt

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									           Class Gastropoda
•   Snails - largest class of molluscs
•   ~ 85,000 living spp.
•   ~ 15,000 fossil spp.
•   Habitats: marine benthos, ocean
    plankton, freshwater, land
   Gastropod characteristics
• 1. Torsion - primitive bilateral symmetry
  lost during development
• Twisting of visceral mass, mantle, and
  mantle cavity

                        After torsion
     Gastropod characteristics
•   2. Definite head: eyes, tentacles
•   3. Flat ventral foot
•   4. Mantle cavity w/gills or lungs
•   5. Buccal cavity w/ radula
          Characters cont.
• 6. Coiled shell - one continuous
  piece
  – operculum on posterior foot of
    some
             plano-spiral
                                     helico-spiral
        Characters, cont.
• 7. Centralized complex nervous system
• 8. Hermaphroditic or dioecious
• 9. Oviparous or ovoviparous
          10. Larval form
• Archaeogastropoda have trochophore
  larva
• Many marine snails have veliger larva
• Freshwater + terrestrial species usually
  hatch as young snails
      Gastropod classification
•   3 subclasses:
•   Prosobranchia
•   Opisthobranchi - reduced shell
•   Pulmonata - lungs
      Subclass Prosobranchia
•   Mantle cavity anterior
•   1 or 2 gills
•   shell and operculum usually present
•   most are dioecious
         Prosobranchs, Order
         Archaeogastropoda
•   Primitive snails
•   External fertilization
•   Trochophore larva
•   2 bipectinate gills
•   2 auricles
•   2 coelomoducts
      Prosobranchs, Order
      Archaeogastropoda
• A. slit shells - deep water species
  – Abalones (Haliotis)
  – 9 spp on our Pacific coast
  – Commercially harvested
      Prosobranchs, Order
      Archaeogastropoda
• B. keyhole limpets - Fissurella
  – conical shells




• C. Limpets - Acmaea
       Prosobranchs, Order
       Archaeogastropoda
• D. topshells, turban shells, star shells
  – Astraea
       Prosobranchs, Order
       Archaeogastropoda
• E. Nerites (Nerita) intertidal in Caribbean
  – some freshwater + terrestrial
         Prosobranchs, Order
           Mesogastropoda
•   Male with penis
•   Fertilization internal
•   1 monopectinate gill
•   1 auricle
•   1 coeloduct
      Prosobranchs, Order
        Mesogastropoda
• A. Freshwater apple snails -
  – Viviparus, Pomacea
      Prosobranchs, Order
        Mesogastropoda
• B. Turret shells - worm shells; caecums,
  ceriths, some freshwater genera, all
  have high shells
      Prosobranchs, Order
        Mesogastropoda
• C. Violet snails - pelagic grazers on
  man o’war
  – Vellela, Porpita
  – Janthina: secretes bubble mass for
    floatation
       Prosobranchs, Order
         Mesogastropoda
• D. Cap shells, slipper shells
  – Crepidula change sex w/age
     • see slides of veliger larva
      Prosobranchs, Order
        Mesogastropoda
• E. Conchs - Strombus
  – Feed on algae, turtlegrass
  – Commercial harvest in Caribbean
       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
Cowries
      Prosobranchs, Order
        Mesogastropoda
• G. Heteropods - pelagic, swimming
  snails w/reduced shell
• Carinaria (see Fig. 10-30, p. 399)
      Prosobranchs, Order
        Mesogastropoda
• H. Moon shells - predators on molluscs:
  – bore into shells
  – Lunatia
  – Polinices
            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
        Prosobranchs, Order
          Mesogastropoda
•   I. Helmet shells, tritons, tuns
•   Predators on molluscs and echinoderms
•   Long proboscis
•   Large shells
       Prosobranchs, Order
         Mesogastropoda
• J. Periwinkles - intertidal
  – Littorina
      Prosobranchs, Order
        Neogastropoda
• Mostly same characteristics as
  Mesogastropoda
• Radula has only 3 teeth in a transverse
  row
• Most are marine
• Most are carnivores
      Prosobranchs, Order
        Neogastropoda
• A. Drills - Murex, Urosalpinx
• Drill holes in shells of bivalves and
  barnacles
• Oyster drill and others cause economic
  losses
        Prosobranchs,
     Order Neogastropoda
• B. Whelks - Busycon
• Tulip shells - Fasciolaria
• Predators and carrion feeders
         Prosobranchs,
      Order Neogastropoda
• C. Olives, miters, and volutes
• Colorful, mostly tropical snails
• prey on invertebrates
         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
                Conus
• Long proboscis with harpoon-like
  radular tooth
• venom gland
“Glory of the sea” cone shell
   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
   Subclass Opisthobranchia
• A. Bubble shells - Bulla
• Predators with thin, reduced shell
     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
     Subclass Opisthobranchia
•   C. Sea slugs
•   With or w/o shell
•   Berthelinia is a “bivalve” gastropod
•   Fig. 10-23, p. 392
   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
More
Pteropods
   Subclass Opisthobranchia
• E. Nudibranchs
• Often with secondary gills and cerata
  (hornlike dorsal projections)
• Many endemics
  Subclass Opisthobranchia
• F. Parasitic Opisthobranchs
• 2 orders
• One ectoparisitic on bivalves and
  annelids
• One endoparasitic in sea cucumbers
       Subclass Pulmonata
• Charactistics like Opisthobranchia, but
  w/o gill
• Mantle cavity converted to lung
• Shell usually present
• No operculum
• Hermaphroditic
       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
       Subclass Pulmonata
• B. Land snails and slugs
  – Helix
  – Limax




• C. Intertidal slugs w/posterior anus
        Class Scaphopoda
            tusk 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
  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)
Foot
  Scaphopod characteristics
• 4. Radula present
• 5. Circulatory system reduced - sinuses
  – Gills absent
• 6. Dioecious, trochophore and veliger
  larval stages
    Scaphopod classification
• Two families (representative species):
• Dentalium - conical shell

• Cadulus + Siphonodentalium - globular
  shell, enlarged foot

								
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