BIO 385 Invertebrate Zoology
Go To: Udo Savalli | BIO 385 |

Invertebrate Diversity
Phylum Mollusca Molluscs

(Click on any image for larger version)

Mollusc Characteristics

  • Coelom reduced
  • Most viscera concentrated in dorsal visceral mass
  • Body covered by thick mantle (epidermis) which forms a cavity
  • Mantle secretes calcium carbonate shell (or spicules)
  • Large ventral muscular foot
  • Radula (band of teeth in esophagus)
  • Additional classes not covered in lab:
    • Aplacophora
    • Monoplacophora

Class Polyplacophora Chitons


  • Dorso-ventrally flattened and somewhat elongated
  • 8 dorsal shell plates (valves)
  • Mantle forms thick lateral girdle (and sometimes covers plates)
  • Lack eyes, antennae
  • Marine
Conspicuous Chiton
Conspicuous Chiton, Stenoplax conspicua, CA
Lined Chiton
Lined Chiton, Tonicella lineata, CA
Black Chiton
Black Chiton, Katharina tunicata, CA
Veiled Chiton
Veiled (Carnivorous) Chiton, Placiphorella velata
Gumboot Chiton Dorsal
Dorsal view of gumboot chiton, Crytpochiton stelleri, the world's largest species (30 cm); CA
Gumboot Chiton Ventral
Ventral view of gumboot chiton; CA
See also labeled photo.

Class Gastropoda Snails & Slugs


  • Coiled, asymmetric shell (lost in many)
  • Visceral mass (gut, nervous system) becomes twisted 90-180°
  • Muscular, flattened, creeping foot
  • Head with eyes (may be reduced or lost), tentacles
  • Mantle highly vascularized; becomes lung
  • Marine, freshwater, and terrestrial
Limpet Veliger
Veliger (larval) stage of Slipper Limpet, Crepidula sp.; stained whole-mount.
Gastropod Shell
Shell structure of a frogsnail, Bursa sp.
See also labeled photo.
Snail Dissection
Dissection of a Garden Snail, Helix sp.
See also labeled photo.

Order Vetigastropoda

Keyhole Limpet
Giant Keyhole Limpet, Megathura crenulata; San Diego, CA
Red Abalone, Haliotis rufescens
Turban Snail
Turban Snail, Tectus sp.
Turban Snail mouth
Wavy Turban, Megastrea undosa, closeup of mouth and radula

Order Caenogastropoda

Chestnut Cowry
Chestnut Cowry, Cypraea spadicea; San Diego, CA
Flamingo Tongues
Flamingo Tongues, Cyphoma gibbosum; Belize
Carinate Dovesnails, Alia carinata
Dogwinkles, Thais lapillus; ME
Checkered Periwinkle, Littorina scutulata; CA
Kellet's Whelk
Kellet's Whelk, Kelletia kelletii; San Diego, CA
Worm Snail
Scaled Worm Snails, Serpulorbis squamigerus; a tube-dwelling snail that captures food using sticky strands of mucus
Apple Snail
Apple Snail, Pomacea sp., a fresh-water 'prosobranch'

Order Opisthobranchia:

Green Bubble
Green Bubble Snail, Haminoea virescens; note reduced shell; San Diego, CA
Sea Hare
Sea Hare, Aplysia californica, a species with a reduced internal shell; LaJolla, CA
Navanax, Navanax inermis; LaJolla, CA
Yellow Porostome
White-spotted Sea Goddess, Doriopsilla albopunctata; CA
Opalescent Nudibranch
Opalescent Nudibranch, Hermissenda crassicornis; San Diego, CA
Hopkins Rose
Hopkin's Rose, Hopkinsia rosacea; San Diego, CA
Coral-eating Nudibranch
Coral-eating Nudibranch, Tritoniopsis elegans
Lions Mane Nudibranch
Lion's Mane Nudibranch, Melibe leonina

Order Pulmonata:

African Giant Snail
African Giant Snail, Achatina fulica, a large (10-15 cm) terrestrial species; Kenya
Bladder Snail
Pond Snail, Lymnaea sp., a small (8 mm) fresh water species.
Banana Slug
Banana Slug, Ariolimax columbianus; note pneumostome; CA
Unidentified slug; ME
Blue Snail
Unidentified Blue Land Snail; CA
Decollate Snail
Decollate Snail, Rumina decollata; AZ
Wolf Snail
Rosy Wolf Snail, Euglandina rosea; HI

Class Bivalvia Clams, etc.


  • Body and foot laterally compressed
  • Shell with two hinged valves
  • Reduced cephalization
  • Edges of mantle usually fused to form siphons
  • Radula lost
  • Marine and freshwater; mostly filter-feeders
Quahog Shell
Left Valve of a Northern Quahog, Mercenaria mercenaria.
See also labeled photo.
Clam Dissection
Anatomy of a Clam (in right valve).
See also labeled photo.
Bean Clam
Bean Clam, Donax gouldii; note foot & siphons; LaJolla, CA
Flat-tipped Piddocks, Penitella penita, CA
Scale-sided Piddock, Parapholas californica
Blue Mussels
California Mussels, Mytilus californianus; CA
Giant Clam
Fluted Giant Clam, Tridacna squamosa; relies on endosymbiotic algae in its mantle for nutrients
Swimming Scallop, Chlamys sp.
Flame Scallop, Lima scabra (not a true scallop)

Class Scaphopoda Tusk Shells


  • Single tubular, tapered shell
  • Shell open at both ends
  • Anterior adhesive tentacles
  • Benthic marine environments
Tusk Shell
Tusk Shell, Dentalium sp.; shell only

Class Cephalopoda Squid, etc.


  • Shell chambered (if present), reduced, or absent
  • Prehensile tentacles surround mouth
  • Mouth with radula and beak
  • Muscular siphon provides jet propulsion
  • Well developed brain, eyes
  • Closed circulatory system
  • Marine
Large Squid Dissection
Dissections of large, fresh squid, probably Ommastrephes bartramii
See also labeled photo.
Small Squid Dissection
Dissections of small, fresh squid, probably Doryteuthis sp.
See also labeled photo.

Subclass Nautiloidea:

  • Shell chambered (coiled in extant forms, but straight in many fossil forms)
  • 80-90 tentacles surround mouth
  • Shell chambers connected by central siphuncle
  • 6 extant species
  • Marine environments, primarily deep water
Chambered Nautilus
Chambered Nautilus, Nautilus pompilius
Geisomoceras fossil
Fossil Geisonoceras sp., polished (Morocco; Devonian)
Nautiloid fossil
Polished Cymatoceras sp. nautiloid (Madagascar; Cretaceous); note the simple septa

Subclass Ammonoidea:

  • Extinct
  • Chambered shell; sutures that divide chambers have complex shapes
  • Shell usually coiled (but there are exceptions)
  • External shell often marked with knobs and ridges
Binatisphinctes Ammonite
Ammonite fossil, Binatisphinctes rjasanensis, showing external shell and shape of septum (Russia; Late Jurassic Period)
Cleoniceras Ammonite
Ammonite fossil, Cleoniceras sp., showing sutures (Madagascar; late Cretaceous Period)
Cut Ammonite
Cleoniceras sp. ammonite fossil cut to show chambers (Madagascar, early Cretaceous)

Subclass Coleoidea:

  • Shell absent or reduced and internal
  • 8-10 tentacles/arms with suckers
  • Cuttlefish, squid, octopuses
  • Marine
Broadclub Cuttlefish, Sepia latimanus (Order Sepioida)
Flamboyant Cuttlefish
Flamboyant Cuttlefish, Metasepia pfefferi (Order Sepioida)
Pacific Giant Octopus, Enteroctopus dofleini (Order Octopoda)
Market Squid
Common Market Squid, Doryteuthis opalescens (Order Teuthoida)
Giant Squid
Giant Squid, Architeuthis sp., preserved specimen (Order Teuthoida)
Georgia Aquarium, Atlanta
Squid Dissection
Fossil rear guard of Belemnite (Paleocene, Germany) and belemnite model showing guard's approximate position in life
This page last updated 12 December 2016 by Udo M. Savalli ()
Images and text Udo M. Savalli. All rights reserved.