phylum mollusca n.
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Phylum Mollusca. Class Gastropoda. Class Gastropoda. Defining characteristics Visceral mass and nervous system become twisted 90-180 ° during embryonic development Proteinaceous shield on the foot (operculum). Gastropod Morphology and Movement.

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phylum mollusca

Phylum Mollusca

Class Gastropoda


class gastropoda
Class Gastropoda
  • Defining characteristics
    • Visceral mass and nervous system become twisted 90-180° during embryonic development
    • Proteinaceous shield on the foot (operculum)


gastropod morphology and movement
Gastropod Morphology and Movement
  • The typical snail consists of a visceral mass, which sits atop a muscular foot
    • The visceral mass is protected by a univalve shell that is coiled


dextral and sinistral coiling
Dextral and Sinistral Coiling
  • The shell is usually carried on the left side of the body and coils to the right (dextral)
  • Few species are sinistral
    • Shell coils to the left (lightning whelk)




subclass prosobranchia
Subclass Prosobranchia
  • Defining characteristic
    • Mantle cavity generally anterior due to torsion
    • Usually have protective shells
  • Includes most marine gastropods

Oyster Drills


prosobranchia anatomy
Prosobranchia Anatomy
  • Molluscan gill
    • Ctenidium, consists of a series of flattened, triangular sheets
    • Water is drawn into the animal by gill cilia
    • Osphradium





  • Life begins as a trochophore larvae which then develops into a veliger larvae
    • The veliger is where most of the organ systems develop
    • During development the process of torsion begins


local representatives
Local Representatives
  • Banded Tulip (Fasciolaria tulipa)
  • Knobbed Whelk (Busycon carica)

True & Banded Tulip


subclass opisthobranchia
Subclass Opisthobranchia
  • Defining characteristic
    • Mantle cavity located posteriorly due to detorsion
    • Sea slugs and sea hares


nudibranchs sea slugs sea hares
Nudibranchs, Sea slugs, & Sea hares
  • A radula and foot for creeping is usually present (sea slugs)
  • Some have parapodia used for swimming
  • Well developed head and sensory tentacles

Anemone Sea Slug


lemon nudibranch
Lemon Nudibranch

Nudibranchs have no shell or mantle cavity

Lack gills, instead have respiratory projections on the dorsal surface


subclass comparisons
Subclass comparisons
  • Different from prosobranchia:
    • Reduction or loss of the shell and operculum
    • Limited torsion
    • Reduction or loss of the mantle cavity
    • Reduction or loss of ctenida
    • Many have evolved different respiratory structures which are unrelated to ctenidia


local species
Local species
  • Sooty sea hare (Aplysia brasiliana)
    • Have large swimming parapodia and a greatly reduced shell on the back