molluscs

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molluscs

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

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