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Phylum: Mollusks

Phylum: Mollusks. Three Classes of Mollusks. Class Gastropoda – snails, slugs Class Bivalvia – clams, oysters, mussels, scallops Class Cephalopoda –  octopi, squids and cuttlefishes. Basic information. Over 100,000 living species Marine, fresh water, and land Most Bilateral symmetry.

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Phylum: Mollusks

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  1. Phylum: Mollusks

  2. Three Classes of Mollusks • Class Gastropoda – snails, slugs • Class Bivalvia – clams, oysters, mussels, scallops • Class Cephalopoda –  octopi, squids and cuttlefishes

  3. Basic information • Over 100,000 living species • Marine, fresh water, and land • Most Bilateral symmetry

  4. Body Plan • Divided into two regions: • head/foot • visceral mass

  5. Head/foot • Head (contains mouth and variety of sensory structures) • Foot (muscular organ used for locomotion)

  6. Visceral Mass • heart • digestion • excretion • reproduction

  7. Mantle • Covers and protects the visceral mass • Secretes shell

  8. mantle cavity • Location of gills • Space between the mantle and the visceral mass

  9. nervous system • Ganglia: paired cluster of nerve cells • locomotion • feeding • process sensory information (light, touch)

  10. Feeding • Radula: flexible, tongue like strip of tissue covered with tough abrasive teeth that point backward

  11. Class Gastropoda

  12. Basic Information • Most diverse class of mollusks • 90,000 species • Snails, abalones, conches= single shell • Slugs and nudibranchs= no shell

  13. Torsion • Visceral mass twists around 180° in relation to the head • Twisting results in mantle cavity, gills, and anus to the front of the animal • Gastropod is now able to with drawl its head into mantle cavity when threatened

  14. Movement • foot secrets a substance allowing animal to glide over surfaces (Slime Trail)

  15. Open circulatory system • HEMOLYMPH (blood in an organism with open circulation) does not remain in vessels • Collected from gills or lungs • Pumped through heart • Released directly into spaces in the tissues • Fluid filled spaces or blood cavity

  16. Bivalvia: Clams Other Bivalvia: scallops, mussels, oysters

  17. Characteristics • Sessile • Filter feeders • No radula • No cephalization • Aquatic

  18. Anatomy of Valves • Shell is divided into two halves (valves) • Connected by a hinge • Adductor muscles • Contract: close valves • Relax: open vlaves

  19. Clam Sensory information • 3 pairs of ganglia • mouth (cerebral) • digestive system (visceral) • Foot (pedal)

  20. Foot • Foot helps burrow in the sand or mud

  21. Water flow • water enters through incurrent siphon • Water exits through excurrent siphon

  22. Steps in digestion: Filter Feeders 1. Cilia in gills set up water current 2. Gills filter water for small organisms 3. Palps: flaplike structures that surround & guide food into the clam's mouth 4. Food then enters the mouth

  23. Steps in Digestion: Filter Feeders 4. Stomach: Digestion begins 5. Digestive glands: digested particles are absorbed 6. Intestines: collects and removes digestive wastes 7. Waste are passed through the rectum and excreted through anus

  24. Function of Gills • Trap food particles • Exchange oxygen and carbon dioxide

  25. Growth rate • Umbo oldest part of the clam • Growth rings

  26. CLASS CEPHALOPODAMost advanced class

  27. Cephalopod “Head-foot” • foot is concentrated in the head region • foot is modified into arms and tentacles equipped with suckers • Foot also forms funnel (siphon) for expelling water, allowing movement by "jet propulsion"

  28. Squid

  29. Cuttlefish

  30. The major distinction between the squid and octopus Squid Suction Cups Squid suction cups are armed with hooks or sucker rings (or a combination of the two). Octopus have simple suction cups without secondary armature. Tentacle club of Architeuthis, showing circular-saw-like sucker rings. tentacle club of Mesonychoteuthis, with swiveling hooks.

  31. Profile of Mesonychoteuthis tentacle club, showing hooks. Suction cups of Haliphron atlanticus, the giant gelatinous octopus (the world's largest species of octopus), lacking secondary armature.

  32. Giant Squid Can reach length of up to 60 feet and weight of more than 3.5 tons. Architeuthis dux

  33. Nautilus

  34. Octopus

  35. Locomotion • Jet propulsion by using siphon to force water out • Crawling – octopus *Also uses siphon

  36. External Features • Octopus: 8 arms with either one or two rows of suction cups (but never hooks or sucker rings), • Squid/cuttlefish: 10 appendages containing suction cups (contain either hooks or sucker rings) • 8 arms • 2 tentacles

  37. Ink • All except nautilus have ink sack which empties into rectum; ink contains the pigment melanin (same pigment as human skin) • Released when the animal is alarmed. The animal quickly departs from the scene leaving the ink as a decoy to the predator.

  38. Color Changes • Chromatophores – pigment cells that expand and contract to produce color change. • Used as danger signals, protective coloring, and for courtship. The Blue Ringed Octopus (found in shallow coral and rock pools of Australia): It’s poisonous saliva is 10,000 more potent than cyanide. This octopus is only the size of a golf ball but carries enough poison to kill 26 humans in minutes.

  39. Feeding Fish, other mollusks, crustaceans, worms Beak like jaws and radula tear prey into pieces Octopus and Cuttlefish have poison in saliva

  40. Circulatory • Closed circulatory system • Blood delivers oxygen and nutrients directly to organs through veins and arteries

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