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Phylum Mollusca

Phylum Mollusca. chitons, clams, snails, slugs, octopi, cuttlefish, squid, & nautili second largest phylum (50,000+ species) well known fossil record marine, fresh water, and terrestrial. General Characteristics. mostly bilateral symmetry unsegmented eucoelomates; protostomes

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Phylum Mollusca

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  1. Phylum Mollusca • chitons, clams, snails, slugs, octopi, cuttlefish, squid, & nautili • second largest phylum (50,000+ species) • well known fossil record • marine, fresh water, and terrestrial

  2. General Characteristics • mostly bilateral symmetry • unsegmented • eucoelomates; protostomes • great size variation • great diversity & adaptive radiation

  3. Body Plan • cephalization • muscular foot; modified as tentacles in cephalopods • mantle- surrounding the viscera; shell secretion & jet propulsion • calcareous shell: protection & support; nacreous layer & periostracum • radula: feeding in herbivorous species • gills: respiration & filter feeding

  4. Radula

  5. Snail Radula

  6. Ctenidia- Gr. “comb”

  7. Physiology/Development • open circulatory system except cephalopods; hemocoel • excretion: metanephridia • nervous system- ganglion • external & internal fertilization

  8. Class Polyplacophora: “chitons” • 800 species • marine • inhabit rocky intertidal zone • dorsoventrally flattened • overlapping dorsal shell plates • herbivores w/ radula

  9. Polyplacophora – “chitons”

  10. Chiton Anatomy

  11. Class Aplacophora

  12. Aplacophora- Diagnostic Features • small, vermiform • deep marine • no shell; calcareous spines • many burrowing or on cnidarians

  13. Monoplacophora

  14. Monoplacophora- continued • all deep marine • single, unhinged, cap-shaped shell • 3-6 ctenidia • ancestor possibly gave rise to other molluscs

  15. Class Gastropoda • largest taxonomic class • 30,000 extant species • snails, nudibranchs, sea hares, and slugs • marine, freshwater, and terrestrial • shell often asymmetrical spiral

  16. columella

  17. Cone Shells

  18. A. heart B. penis D. dart sac E. sperm duct F. oviduct H. digestive gland I. Stomach J. crop K. esophagus L. buccal bulb C. Gastropoda; S.C. Pulmonata

  19. nudibranchs/sea hares

  20. Veliger Larvae

  21. Class Bivalvia • clams, scallops, oysters, and mussels • filter feeding • mantle secretes a shell of CaCO3 • periostracum, prismatic, & nacreous layers

  22. muscular foot intestine gonad hemocoel mantle gills excurrent/incurrent apertures Clam Anatomy

  23. Muscular Foot

  24. clam glochidia

  25. Class Scaphopoda • “Tusk Shells” • openings at both ends • captacula- adhesive feeding tentacles

  26. Class Cephalopoda • octopods, squid, cuttlefish, & Nautilus • ~ 600 species; entirely marine • highly motile- jet propulsion • highly developed nervous system and sensory • shell reduced or entirely absent in octopods; 5-6 Nautilus possess shells

  27. Reproduction/Development • dioecious • internal fertilization; spermatophore • no larval phase • female often broods the eggs before dying

  28. chromatophores

  29. Nautilus

  30. Giant Squid (Architeuthis)

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