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

helico-spiralplano-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 groups:

• Caenogastropoda: includes gilled snails

• Opisthobranchs - reduced shell

• Pulmonata - lungs

Caenogastropoda

• Mantle cavity anterior

• 1 or 2 gills

• shell and operculum usually present

• most are dioecious

Caenogastropoda

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

Caenogastropoda

• B. keyhole limpets - Fissurella– conical shells

• C. Limpets - Acmaea

Caenogastropoda

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

Neritimorpha

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

Prosobranchs

• Male with penis

• Fertilization internal

• 1 monopectinate gill

• 1 auricle

• 1 coeloduct

Prosobranchs

• A. Freshwater apple snails -– Viviparus, Pomacea

Prosobranchs

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

Prosobranchs

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

floatation

Prosobranchs

• D. Cap shells, slipper shells– Crepidula change sex w/age

• see slides of veliger larva

Prosobranchs

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

• 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

• G. Heteropods - pelagic, swimming snails w/reduced shell

• Carinaria (see Fig. 10-30, p. 399)

• 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

• I. Helmet shells, tritons, tuns

• Predators on molluscs and echinoderms

• Long proboscis

• Large shells

• J. Periwinkles - intertidal– Littorina

• Mostly same characteristics as Mesogastropoda

• Radula has only 3 teeth in a transverse row

• Most are marine

• Most are carnivores

• A. Drills - Murex, Urosalpinx

• Drill holes in shells of bivalves and barnacles

• Oyster drill and others cause economic losses

• B. Whelks - Busycon

• Tulip shells - Fasciolaria

• Predators and carrion feeders

• C. Olives, miters, and volutes

• Colorful, mostly tropical snails

• prey on invertebrates

• 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

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

Opisthobranchia

• A. Bubble shells - Bulla

• Predators with thin, reduced shell

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

Opisthobranchia

• C. Sea slugs

• With or w/o shell

• Berthelinia is a “bivalve” gastropod

• Fig. 10-23, p. 392

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

Opisthobranchia

• E. Nudibranchs

• Often with secondary gills and cerata (hornlike dorsal projections)

• Many endemics

Opisthobranchia

• F. Parasitic Opisthobranchs

• 2 orders

• One ectoparisitic on bivalves and annelids

• One endoparasitic in sea cucumbers

Pulmonata

• Charactistics like Opisthobranchia, but w/o gill

• Mantle cavity converted to lung

• Shell usually present

• No operculum

• Hermaphroditic

Pulmonata

• A. freshwater snails: – Lymnaea, Physa, Planorbis– Freshwater limpets

• Most come to surface for air

• Some have developed secondary gills

• Descended from terrestrial ancestors

Pulmonata

• B. Land snails and slugs– Helix– Limax

• C. Intertidal slugs w/posterior anus

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

• 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

• 4. Radula present

• 5. Circulatory system reduced - sinuses– Gills absent

• 6. Dioecious, trochophore and veliger larval stages

Scaphopod characteristics

Scaphopod classification

• Two families (representative species):

• Dentalium - conical shell

• Cadulus + Siphonodentalium - globular shell, enlarged foot