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Phylum Mollusca

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

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  1. Phylum Mollusca Class Gastropoda Gastropods

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

  3. 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 Gastropods

  4. 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) Gastropods

  5. Torsion Gastropods

  6. Subclass Prosobranchia • Defining characteristic • Mantle cavity generally anterior due to torsion • Usually have protective shells • Includes most marine gastropods Oyster Drills Gastropods

  7. Prosobranchia External Anatomy Gastropods

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

  9. Veliger Trochophore Reproduction • 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 Gastropods

  10. Local Representatives • Banded Tulip (Fasciolaria tulipa) • Knobbed Whelk (Busycon carica) True & Banded Tulip Gastropods

  11. Subclass Opisthobranchia • Defining characteristic • Mantle cavity located posteriorly due to detorsion • Sea slugs and sea hares Gastropods

  12. Gas exchange and defense Gastropods

  13. 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 Gastropods

  14. Lemon Nudibranch Nudibranchs have no shell or mantle cavity Lack gills, instead have respiratory projections on the dorsal surface Gastropods

  15. 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 Gastropods

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

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