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Mollusks

Learn about mollusks, a diverse group of animals with soft bodies and shells such as snails, clams, and octopi. Discover their anatomy, feeding habits, reproduction, and economic importance.

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Mollusks

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  1. Mollusks Kingdom Animalia, Phylum Mollusca (means “soft”)

  2. What is a Mollusk? • Soft body with internal or external shell • Ex: snails, slugs, clams, squid, and octopi • Trochophore larva

  3. Body plan: • Foot – takes on many forms • Mantle – covers the body & secretes shell • Shell – (present in most) • Visceral mass – internal organs

  4. General Characteristics • Bilaterally symmetrical • Triploblastic

  5. General Characteristics Con’t • Open circulatory system • Exception is cephalopods have closed circularoty system • Radula usually present (tongue) • Protostomes

  6. Groups of Mollusks Three major classes of mollusks Gastropoda Bivalvia Cephalopoda

  7. Gastropods • “Stomach Foot” • Snails, Slugs, Nudibranchs, Conchs, Whelks, etc. • 35,000+ species

  8. Freshwater, Marine, or Terrestrial • Shell-less or single-shelled • Move by secreting mucous with cilia or use muscular foot

  9. Snail

  10. Slug

  11. Nudibranchs(sea slugs) Check out the nudibranch gallery at nationalgeographic

  12. Gastropod Anatomy

  13. Torsion • “twisted” body • 180 degree rotation of visceral mass • Significance: allows the snail to retract it’s head into the shell first and it’s foot last.

  14. Interesting Facts! • Land snails can lift ten times their own weight up a vertical surface (like a wall). • Largest Snail = Giant African Land Snail • Can weigh 2 pounds!

  15. Defense from Predators • Shells! • But what about poor land slugs and nudibranchs? • Land slugs are usually nocturnal • Some nudibranchs prey on cnidarians and recycle their nematocysts • Some sea hares can squirt ink to hide themselves

  16. Gastropod Feeding • Most are predators or scavengers • Radula: tongue-like organ that scrapes algae or other plant-like material

  17. Radula

  18. Some predatory gastropods have radula modified to pierce prey

  19. Gastropod Respiration • Gas exchange occurs in mantle cavity – gills or diffusion • Siphon- inhalent tube • Where water enters body

  20. Gastropod Circulation • Have open circulatory system • Blood not contained w/in vessels; instead it washes over the body tissues • Blood acts as a hydrostatic skeleton

  21. Nervous System • Nerves concentrated into large ganglia • Most ganglia located in head region • Simple or complex eyes • Osphradia- chemoreceptors that help to detect prey

  22. Excretion • Nephridium- kidneys • Ammonia = primary nitrogenous waste produced in aquatic species • Uric acid = primary nitrogenous waste produced in terrestrial species

  23. Reproduction • Can be monoecious or dioecious • Usually external fertilization where sperm and eggs released into water • Some internal fertilization in snails

  24. Snail Reproduction

  25. Economic Importance • Delicious-Escargot • Intermediate host for different parasites • Snails and slugs can be serious agricultural pests

  26. Class Bivalvia

  27. General Characteristics • Includes clams, oysters, mussels, scallops • Two shells • Hence “Bi-valvia”

  28. 30,000+ species • Marine and Freshwater • Mostly filter feeders

  29. Interesting Facts! • Largest bivalve -734 pounds and 4 long • Ocean Quahog can live to be 220 years old!

  30. Bivalve Respiration • Incurrent and Excurrent Siphons • Water enters and exits here • Gills greatly expanded and cilliated

  31. Circulation • Open Circulatory System • Blood not contained w/in vessels • Blood “washes” over body tissues by action of the beating heart

  32. Bivalve Feeding and Digestion • Filter feeders • Labial palps filter out food particles • Non-edible particles flushed out through the excurrent siphon

  33. Nervous System Con’t • Most sensory organs are located in the margin of the mantle • Have ganglia • Statocysts and Chemoreceptors

  34. Reproduction • Mostly Dioecious • Gonads located in visceral mass • External fertlization

  35. Economic Importance • Mmm Tasty! • Pearl production • Multi-billion dollar industry

  36. Class Cephalopod

  37. Cephalopods • octopi, squids, cuttlefish, and nautilus • soft-bodied , head is attached to foot • foot is divided into tentacles with sucking disks • Use jet propulsion

  38. Cephalopod Shell • Nautilius only one with external shell • Internal in squid (pen) and cuttlefish (cuttlebone) • Absent in octopi

  39. Movement • Use siphon for jet propulsion • Squeeze mantle cavity forcefully • Sometimes have external “wings” used to help steer

  40. Feeding • Active predators • Many hunt at night • Food captured by tentacles and brought to mouth • Jaws and radula used

  41. Respiration & Circulation • Closed circulatory system • 3 Hearts • Blood is contained w/in vessels • Respiration through gills • High metabolic rate

  42. Nervous System • Very large brain • Advanced, large eyes • Chemoreceptors • Chromatophores-pigment cells • Some of the smartest animals on the planet

  43. Some display bioluminescence: use ATP to light up • squid: brown or black ink

  44. Octopus(creeps on tentacles)

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