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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. After torsion. Gastropod characteristics. 1. Torsion - primitive bilateral symmetry lost during development

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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
gastropod characteristics

After torsion

Gastropod characteristics
  • 1. Torsion - primitive bilateral symmetry lost during development
  • Twisting of visceral mass, mantle, and mantle cavity
slide3

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

plano-spiral

helico-spiral

Characters cont.
  • 6. Coiled shell - one continuous piece
    • operculum on posterior foot of some
characters cont1
Characters, cont.
  • 7. Centralized complex nervous system
  • 8. Hermaphroditic or dioecious
  • 9. Oviparous or ovoviparous
10 larval form
10. Larval form
  • Archaeogastropoda have trochophore larva
  • Many marine snails have veliger larva
  • Freshwater + terrestrial species usually hatch as young snails
gastropod classification
Gastropod classification
  • 3 groups:
  • Caenogastropoda: includes gilled snails
  • Opisthobranchs - reduced shell
  • Pulmonata - lungs
caenogastropoda
Caenogastropoda
  • Mantle cavity anterior
  • 1 or 2 gills
  • shell and operculum usually present
  • most are dioecious
caenogastropoda1
Caenogastropoda
  • A. slit shells - deep water species
    • Abalones (Haliotis)
    • 9 spp on our Pacific coast
    • Commercially harvested
caenogastropoda2
Caenogastropoda
  • B. keyhole limpets - Fissurella
    • conical shells
  • C. Limpets - Acmaea
caenogastropoda3
Caenogastropoda
  • D. topshells, turban shells, star shells
    • Astraea
slide12

Neritimorpha

  • E. Nerites (Nerita) intertidal in Caribbean
    • some freshwater + terrestrial
prosobranchs
Prosobranchs
  • Male with penis
  • Fertilization internal
  • 1 monopectinate gill
  • 1 auricle
  • 1 coeloduct
prosobranchs1
Prosobranchs
  • A. Freshwater apple snails -
    • Viviparus, Pomacea
prosobranchs2
Prosobranchs
  • B. Turret shells - worm shells; caecums, ceriths, some freshwater genera, all have high shells
prosobranchs3
Prosobranchs
  • C. Violet snails - pelagic grazers on man o’war
    • Vellela, Porpita
    • Janthina: secretes bubble mass for floatation
prosobranchs4
Prosobranchs
  • D. Cap shells, slipper shells
    • Crepidula change sex w/age
      • see slides of veliger larva
prosobranchs5
Prosobranchs
  • E. Conchs - Strombus
    • Feed on algae, turtlegrass
    • Commercial harvest in Caribbean
slide19
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
slide22
H. Moon shells - predators on molluscs:
    • bore into shells
    • Lunatia
    • Polinices
moon shells
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
slide24
I. Helmet shells, tritons, tuns
  • Predators on molluscs and echinoderms
  • Long proboscis
  • Large shells
slide26
Mostly same characteristics as Mesogastropoda
  • Radula has only 3 teeth in a transverse row
  • Most are marine
  • Most are carnivores
slide27
A. Drills - Murex, Urosalpinx
  • Drill holes in shells of bivalves and barnacles
  • Oyster drill and others cause economic losses
slide28
B. Whelks - Busycon
  • Tulip shells - Fasciolaria
  • Predators and carrion feeders
slide29
C. Olives, miters, and volutes
  • Colorful, mostly tropical snails
  • prey on invertebrates
slide30
D. Cones - Conus
  • Most prey on inverts
  • Those that prey on fish can be dangerous to humans
  • Fig 10-42, p. 409
conus
Conus
  • Long proboscis with harpoon-like radular tooth
  • venom gland
opisthobranchia
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
opisthobranchia1
Opisthobranchia
  • A. Bubble shells - Bulla
  • Predators with thin, reduced shell
opisthobranchia2
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
opisthobranchia3
Opisthobranchia
  • C. Sea slugs
  • With or w/o shell
  • Berthelinia is a “bivalve” gastropod
  • Fig. 10-23, p. 392
opisthobranchia4
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
slide38

More

Pteropods

opisthobranchia5
Opisthobranchia
  • E. Nudibranchs
  • Often with secondary gills and cerata (hornlike dorsal projections)
  • Many endemics
opisthobranchia6
Opisthobranchia
  • F. Parasitic Opisthobranchs
  • 2 orders
  • One ectoparisitic on bivalves and annelids
  • One endoparasitic in sea cucumbers
pulmonata
Pulmonata
  • Charactistics like Opisthobranchia, but w/o gill
  • Mantle cavity converted to lung
  • Shell usually present
  • No operculum
  • Hermaphroditic
pulmonata1
Pulmonata
  • A. freshwater snails:
    • Lymnaea, Physa, Planorbis
    • Freshwater limpets
  • Most come to surface for air
  • Some have developed secondary gills
  • Descended from terrestrial ancestors
pulmonata2
Pulmonata
  • B. Land snails and slugs
    • Helix
    • Limax
  • C. Intertidal slugs w/posterior anus
class scaphopoda tusk shells
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
scaphopod characteristics
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)
scaphopod characteristics1
Scaphopod characteristics
  • 4. Radula present
  • 5. Circulatory system reduced - sinuses
    • Gills absent
  • 6. Dioecious, trochophore and veliger larval stages
scaphopod classification
Scaphopod classification
  • Two families (representative species):
  • Dentalium - conical shell
  • Cadulus + Siphonodentalium - globular shell, enlarged foot