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molluscs

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  • 1. Phylum Mollusca Examples
  • 2. General Information
    • Coelom (Mollusca = space around heart)
    • 90,000 living species (aquatic & terrestrial)
    • 8 living classes
    • Mostly marine, but found from bottom of the oceans to 7000 meters above sea level in ponds, lakes, streams, forests, grasslands, & other environments.
    • Microscopic to 20 meters and 2000 pounds
    • Terrestrial forms need humidity, shelter, and calcium rich soils.
  • 3. More general info
    • Fundamentally bilaterally symmetric, torsion
    • Head-foot & visceral mass , more about forms
    • Gills, open/closed circ., hemocyanin
    • Protective mantle (secretes shell)
    • Mantle cavity houses gills (ctenidia) or lungs
    • Most cephalization @ anterior end
    • Complete digestive system
    • Radula (most mollusca other than bivalves which have labial palps & filter feed)
  • 4. & more…
    • Foot
    • Shell (3 layers)
      • Periostracum - outer, conchiolin (protein)
      • Prismatic layer - middle, CaCO 3
      • Nacreous layer - inner, CaCO 3 (crystalline) m.o.p.
    • Reproduction
      • Most dioecious (some monoecious - protandrous)
      • Egg - Juvenile (cephalopoda)
      • Egg -Trochophore - Juvenile (Chitons)
      • Egg -Trochophore - Veliger - Juvenile (bivalvia, gastropoda)
  • 5. Generalized Trochophore Larva
  • 6. Human impact
    • Food
    • Jewelry ( pearls , shells, mother of pearl)
    • Pests
      • Agricultural damage: Snails
      • Wood destruction: Ship worms
      • Fouling: Zebra mussels
    • Parasite intermediate hosts (e.g. Flukes)
  • 7. Classes
    • Caudofoviata
    • Solenogastres
    • Monoplacophora
    • Polyplacophora
    • Scaphopoda
    • Gastopoda
    • Bivalvia
    • Cephalopoda
  • 8. Caudofoveata
    • Primitive wormlike molluscs
    • 120 species
    • 2 to 140 mm long
    • Benthic, living in sediment
    • Feed on microorganisms & detritus
    • Calcareous scales
    • Radula
    • Dioecious
  • 9. Solenogastres
    • Wormlike
    • Shelless with scales or spicules
    • 250 Marine species
    • Reduced head, No radula, No gills
    • No nephridia
    • Monoecious
    • Bottom dwelling without burrows
    • Feed on cnidarians
  • 10. Class Monoplacophora
    • Small, low, rounded shell & Creeping foot
    • Serial repetition of organs (segmentation)
    • 25 species
    • Dioecious
    • Sea floor
    • 3 - 6 pairs of gills
    • 3 - 7 pairs of metanephridia
    • Ladder-like nervous system
    • Radula
  • 11. Polyplacophora (plate bearers)
    • Flattened dorsoventrally with 8 articulating plates - roll up for protection
    • About 1000 species ( Chitons )
    • Most 2 - 5 cm, One species 30 cm.
    • Reduced head/cephalic structures
    • Photosensitive esthetes
    • Chemoreceptive osphradia in mantle groove
    • Most rocky intertidal regions (some deep)
    • Feed on algae with radula (magnetite)
    • 3-chambered heart, kidneys, long. nerve cord
    • Dioecious, Egg-Trochophore-Juvenile. No veliger.
  • 12. Class Gastropoda
    • Largest class (70,000)
      • Snails, slugs, whelks, conchs, periwinkles, sea slugs, sea hares, & sea butterflies
    • One piece shell (when present)
    • Coiled or not (whorls) Dextral or Sinistral (genetic)
    • Asymmetric due to torsion
    • Microscopic to 60 cm. long
    • Marine, freshwater, terrestrial
    • Climb, swim, burrow
  • 13. Gastropoda contd.
    • Defense
      • Shell (most)
        • Operculum (aperture)
      • Venom
      • Cnidocytes
      • Toxic secretions
        • Slugs
      • Foot (Strombus sp.)
        • Like hammer
    • Feeding
      • Usually with radula
      • Venom (conotoxins)
      • External stomach
  • 14. Gastropod Groups
    • Prosobranchs
    • 1  Marine snails, some fw & terrestrial sp.
    • E.g. abalones, limpets, conchs
    • To 24”
    • Torsion
    • Anterior mantle cavity
    • Waste exits holes (abalone, limpet) to avoid fouling gills
    • Opisthobranchs
    • 1  Marine
    • Sea slugs, s. hares, s. butterflies, & bubble shells
    • Complete detorsion
    • Shell reduced or absent
    • Monoecious
    • 2 pr. Tentacles (rhinophores)
  • 15. Gastropods cont.
    • Pulmonates
    • 1º Terrestrial snails & slugs
    • Lungs rather than ctenidia
    • Pneumostome
    • Waste expelled forcibly from anus & Nephridiopore
    • Monoecious
    • 2 pr. Tentacles
    • Eyes on second pr.
  • 16. Class Bivalvia
    • Mussels, clams, scallops & shipworms
    • 1mm to 1M and 500+ pounds (Tridacna)
    • Sedentary filter feeders (No radula) fig. 16-31
    • Posterior siphons
    • Little cephalization
    • 1º marine, some brackish & fw species
    • Two shells, laterally compressed, hinged dorsally
    • Produce pearls (Nacre)
    • Usually dioecious, some Monoecious (protandrous)
    • Egg, trochophore, veliger (glochidium), juvenile
  • 17. Bivalvia contd.
    • Reproduction
      • Marine bivalves: most dioecious, ext. fertilization E.G…
        • (oyster) Egg - trochophore - veliger - spat - juvenile
      • Freshwater clams: dioecious, int. fertilization
        • Egg - glochidia larvae (parasite) - juvenile; Lure
    • Boring bivalves, e.g.. Teredo, Bankia
      • Small anterior valves @ anterior end = rasp
      • Bacteria digest cellulose & fix nitrogen!
      • Some rock boring species!
  • 18. Bivalve life cycle This one!
  • 19. Class Cephalopoda
    • Squids , octopuses, nautiluses, & cuttlefish
    • 2 cm to almost 60 ft.
    • Large head, conspicuous eyes; 10” (giant squid)
    • Nautilus - external shell; siphuncle more
      • Up to 90 tentacles! Sticky no suckers
    • Cuttlefish, squid - internal shell (pen)
      • 8 arms, 2 tentacles
    • Octopus - no shell
      • 8 arms
    • Organs
    • Locomotion by siphon (ventral funnel) & arms
  • 20. Class Cephalopoda contd.
    • Closed circulatory system, hemocyanin
    • Accessory (branchial) hearts pressurize blood to gills
    • NS: Large brain, Giant axons, eyes, statocysts, tactile sense, no hearing
    • Learning by observation!
    • Communication by primarily by vision ( chromatophores ) and tactile sense
  • 21. … and more cephalopods
    • Defense: camouflage, ink gland (sepia)
    • Separate sexes
    • Male hectocotylus (modified arm) for Transmittal of spermatophore near oviduct (Nautilus = spadix)
    • Eggs fertilized on the way out
    • Octopuses brood eggs, squid eggs, nautilus, cuttlefish eggs