Class Gastropoda

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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

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Gastropod characteristics

• 1. Torsion - primitive bilateral symmetry lost
  during development
• Twisting of visceral mass, mantle, and mantle
  cavity

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Gastropod characteristics

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

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Characters cont.

• 6. Coiled shell - one continuous piece
• operculum on posterior foot of some

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Characters, cont.

• 7. Centralized complex nervous system
• 8. Hermaphroditic or dioecious
• 9. Oviparous or ovoviparous

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10. Larval form

• Archaeogastropoda have trochophore larva
• Many marine snails have veliger larva
• Freshwater terrestrial species usually hatch as
  young snails

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Gastropod classification

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

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Caenogastropoda

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

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Caenogastropoda

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

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Caenogastropoda

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

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Caenogastropoda

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

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Neritimorpha

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

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Prosobranchs

• Male with penis
• Fertilization internal
• 1 monopectinate gill
• 1 auricle
• 1 coeloduct

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Prosobranchs

• A. Freshwater apple snails -
• Viviparus, Pomacea

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Prosobranchs

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

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Prosobranchs

• C. Violet snails - pelagic grazers on man owar
• Vellela, Porpita
• Janthina secretes bubble mass for floatation

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Prosobranchs

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

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Prosobranchs

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

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• 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

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

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

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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

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

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• J. Periwinkles - intertidal
• Littorina

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

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

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

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

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

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Conus

• Long proboscis with harpoon-like radular tooth
• venom gland

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Glory of the sea cone shell
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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

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Opisthobranchia

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

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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

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Opisthobranchia

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

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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

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More Pteropods
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Opisthobranchia

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

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Opisthobranchia

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

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Pulmonata

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

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Pulmonata

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

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Pulmonata

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

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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

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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)

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Foot
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Scaphopod characteristics

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

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Scaphopod classification

• Two families (representative species)
• Dentalium - conical shell
• Cadulus Siphonodentalium - globular shell,
  enlarged foot