Gastropod Characteristics
- Snails & Slugs
- Coiled, asymmetric shell (lost in many)
- Visceral mass (gut, nervous system) becomes twisted 90-180° (reversed in some)
- Muscular, flattened, creeping foot
- radula well developed
- Head with eyes (may be reduced or lost) & tentacles
- Marine, freshwater, and terrestrial
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Veliger (larval) stage of Slipper Limpet, Crepidula sp.; stained whole-mount.
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Dissection of a Garden Snail, Helix sp.
See also labeled photo.
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Snail radula surface view (stained slide)
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Order Vetigastropoda
Characteristics
- Most primitive group of extant gastropods
- Many (but not all) have excurrent slit or openings in shell
- United by details of microscopic shell structure, gill structure, and molecular evidence
- Most are grazers on algae or on sessile animals such as bryozoans and sponges
- All are marine
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Giant Keyhole Limpet, Megathura crenulata; San Diego, CA
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Red Abalone, Haliotis rufescens
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Turban Snail, Tectus sp.
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Wavy Turban, Megastrea undosa, closeup of mouth and radula
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Emperor's Slit Shell, Pleurotomaria hirasei (Order Vetigastropoda); note slit for water outflow
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Ass's Ear Abalone Shell, Haliotis asinina (Order Vetigastropoda); note openings for water outflow
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Other Gastropod Orders
Order Patellogastropoda
Characteristics
- True limpets
- All have conical, uncoiled, cone-shaped shells (but lack apical opening of the limpet-like Vetigastropoda; the limpet-like shell as also evolved independently in other Gastropod groups)
- Generally use suction to adhere to rocks and other substrates
- Grazers on algae and sea weeds
- Found primarily in the rocky intertidal zone, but some in deep sea
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Seaweed Limpets, Discurria insessa, feeding on kelp; CA
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Plate Limpets, Lottia scutum
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Southern Ribbed Limpets, Lottia austrodigitalis; CA
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Order Neritimorpha
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Characteristics
- Nerites
- Typical-looking gastropod snails
- Most have coiled shell with a low spire, but some with limpet-like shell
- Operculum present
- Includes marine, fresh water, and a few land snails
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Horned Nerite, Clithon corona; a freshwater species
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Nerite shell, Nerita sp.; a marine species
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Spotted Nerite shell and operculum, Neritina natalensis
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Order Caenogastropoda
Characteristics
- Typical marine snails
- Large and diverse group (60% of all extant gastropods)
- Nearly all have shells (exceptions are some obscure parasites); shells are usually coiled
- Operculum is present
- Characterized by details of radula, heart and ctenidia and molecular data
- Mostly marine, but some fresh water and terrestrial species
Chestnut Cowry, Cypraea spadicea; San Diego, CA
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Flamingo Tongues, Cyphoma gibbosum; Belize
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Carinate Dovesnails, Alia carinata
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Dogwinkles, Thais lapillus; ME
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Nassa Mud Snail, Nassarius vibex;
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Tiger Sand Conch, Strombus sp.
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Checkered Periwinkle, Littorina scutulata; CA
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Scaled Worm Snails, Serpulorbis squamigerus; a tube-dwelling snail that captures food using sticky strands of mucus
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Apple Snail, Pomacea sp., a fresh-water 'prosobranch'
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Gastropod Shell Diversity (Caenogastropoda)
Shell structure of a frogsnail, Bursa sp.
See also labeled photo.
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Cut shell of a Strawberry Conch, Strombus luhuanus, showing columella
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Sinistral vs. dextral shells: the sinistral Perverse Lightning Whelk, Sinistrofulgur perversum, is on the left and the dextral Channel Whelk, Busycon canaliculatum, is on the right (both family Buccinidae)
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Two views of the shell of Lewis's Moonsnail, Neverita lewisii; arrow indicates the umbilicus at the base of the columella.
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Cone Shells, from left to right: Unid. Cone (Conus sp.), Captains Cone (Conus capitaneus), Alphabet Cone (Spuriconus spurius), Lettered cone (Conus litteratus) (Order Caenogastropoda)
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Tiger Cowry, Cypraea tigris, ventral view; Map Cowry, Leporicypraea mappa, dorsal view (Order Caenogastropoda); both are tubular shells
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Gastropod Shells, left to right: West Indian fighting conch, Strombus pugilis; Horn snail, Batillaria sp.; and Spiral babylon, Babylonia spiralis (Order Caenogastropoda)
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Spider Conch Shell, Lambis lambis (Order Caenogastropoda)
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Venus Comb Shell, Murex pecten (Order Caenogastropoda); note operculum
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Common Slipper Shells, Crepidula fornicata showing ventral and dorsal views; the shelf is a site of muscle attachment (Order Caenogastropoda)
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Worm Snail Shell, Tenagodus sp. (Order Caenogastropoda); this shell represents a different family than shown above and thus is an independent evolution of loosely coiled worm-tube-like shells
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A string of egg cases from a whelk, Busycon sp.? (Order Caenogastropoda)
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Clade Heterobranchia
A monophyletic group that includes the nudibranchs, pulmonates, and several smaller taxa. Divisions within this group are still being worked out. The various "sea slugs" were formerly placed in the Opisthobranchia, but this group is likely polyphyletic.
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Order Nudibranchia
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Characteristics
- Nudibranch sea slugs
- Lack shells
- Lack ctenidia: respire through mantle with aid of cerata and/or external gills
- Many are colorful
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White-spotted Sea Goddess, Doriopsilla albopunctata; CA
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Opalescent Nudibranch, Hermissenda crassicornis; San Diego, CA
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Spanish Shawl, Flabellina iodinea; La Jolla, CA
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Hopkin's Rose, Hopkinsia rosacea; San Diego, CA
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Coral-eating Nudibranch, Tritoniopsis elegans
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Lion's Mane Nudibranch, Melibe leonina
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Black-tipped Spiny Doris, Acanthodoris rhodoceras; San Diego, CA
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Cockerell’s Dorid, Limacia cockerelli; San Diego, CA
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Porter's Chromodorid, Mexichromis porterae; San Diego, CA
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Clade Euopisthobranchia
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Characteristics
- Sea slugs that are not nudibranchs, including bubble shells and sea hares
- Formerly considered part of the "Opisthobranchia"
- Mostly united by DNA
- Sea slug-like, but typically with reduced or soft, internal shells
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Green Bubble Snail, Haminoea virescens; note reduced shell; San Diego, CA
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Sea Hare, Aplysia californica, a species with a reduced internal shell; LaJolla, CA
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Navanax, Navanax inermis; LaJolla, CA
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Order Pulmonata (Clade Panpulmonata)
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Characteristics
- Pulmonate snails and their relatives
- Typical land and fresh-water snails and slugs
- Most with coiled shell; lack operculum
- Some (such as land slugs) have lost their shell
- Mantle cavity forms an enclosed "lung" for respiration
- The clade includes some marine species
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Agate Snail, Limicolaria sp., a large terrestrial species; Kenya
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Pond Snail, Lymnaea sp., a small (8 mm) fresh water species.
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Western Dusky Slug, Arion subfuscus; ME
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Button's Banana Slug, Ariolimax buttoni; note pneumostome; CA
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Draparnaud's Glass Snail, Oxychilus draparnaudi; CA
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Decollate Snail, Rumina decollata; AZ
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Rosy Wolf Snail, Euglandina rosea; HI
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Shells of two pond snails, Lymnaea sp. (dextral) on left; Physa sp. (sinistral) on right
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Lettuce Sea Slug, Elysia crispata: although superficially similar to the nudibranchs, this species is more closely related to the pulmonates (although it lacks the air-breathing lung)
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