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Fascinating World of Molluscs: Diversity Unveiled

Learn about Phylum Mollusca and its vast array of species, from gastropods to bivalves, cephalopods, chitons, and more. Discover their unique characteristics, habitats, and feeding habits in this comprehensive guide to the enchanting world of molluscs.

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Fascinating World of Molluscs: Diversity Unveiled

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  1. 5. Molluscs

  2. Phylum Mollusca • 200,000 species • More species in ocean than any other animal group • Soft body enclosed by calcium carbonate shell • Body covered by mantle • Thin layer of tissue that secretes the shell

  3. Phylum Mollusca • Displays Bilateral Symmetry • Ventral muscular foot used for locomotion • Most had have that includes eyes and other sensory organs

  4. Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.

  5. Phylum Mollusca • Some have radula • Ribbon of small teeth used to rasp food from surfaces • Made of chitin

  6. What’s a radula and how does it work? Modern woodworkers could tell you! micrograph of a mollusc radula: note the chisel-like design

  7. Phylum Mollusca • Have paired gills • Portion of body may be coiled and asymetrical • Occupy all marine environments – rocky shores to hydrothermal vents

  8. Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.

  9. nudibranch, Phidiana crassicornis giant keyhole limpet Megathrua crenulata red abalone Haliotis rufescens Cone snail, Conus geographus Cooper’s nutmeg snail Cancellaria cooperi • Gastropods (Class Gastropoda), or stomach foot, • are the most common mollusks. • Snails, limpets, abalone, and nudibranchs. • 75,000 spp.

  10. Class Gastropod – Stomach Footed • Coiled mass of vital organs enclosed by a dorsal shell resting on a foot

  11. Class Gastropod – Stomach Footed • Most use radula to scrape algae • Mud snails are deposit feeders • Whelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishes • Modified Radula to drill and rasp prey

  12. Class Gastropod – Stomach Footed • Nudibranchs (sea slugs) • No shell • Colorful branches of the gut and gills • Prey on sponges and other invertebrates • Produce noxious chemicals or retain undischarged nematocysts taken undigested from prey

  13. Bivavles: Class Bivalvia

  14. Class Bivalvia • Clams, mussels, and oysters • Body laterally compressed and enclosed with two parts (valves) • No head or radula • Gills expanded and folded used to obtain oxygen, and filter and sort food particles from water

  15. Scallops also filter feed. Many have striking color patters.

  16. Class Bivalvia • Inner surface of shell lined w/ mantle so whole body lies in mantle cavity • Strong muscles used to close valves

  17. Class Bivalvia • Clams burrow in sand or mud and water drawn in and out of mantle by siphons • Allow clam to feed and obtain oxygen while buried

  18. Class Bivalvia • Mussels secrete byssal threads that attach them to rocks and other surfaces

  19. Class Bivalvia • Oysters cement their left shell to hard surface and other to another oyster • Pearls occur when irritating particles are lodged within the mantle cavity and covered by secretions (CaCO3) from oyster

  20. Class Bivalvia • Some scallops can swim by rapidly ejecting water from mantle cavity with siphon

  21. Class Bivalvia • Shipworm bores in mangroves, driftwood, and pilings • Have symbiotic relationship w/ bacteria in the gut that digests wood • Valves lie at the inner end of tunnel lined w/ calcium carbonate and siphon protrudes from entrance • Fouling organism = settles on bottoms of boats, pilings, and other submerged surfaces

  22. Cephalopods “Putting Your Head and Feet Together”

  23. Class Cephalopoda (head footed) • Predators specialized in locomotion • Octopi, squid, and cuttlefish • Agile swimmers w/ complex nervous system and reduction or loss of shell • All are marine

  24. Cephalopod (General Morphology) While still following the basic body plan of a mollusc, octopi are highly specialized.

  25. Cephalopod (General Morphology) • Large eyes on side of head • Thick muscular mantle which protects head • Water enters mantel and leaves through siphon = jet propulsion

  26. Cephalopod: Octopi • Octopi • Eight long arms (2 in to 30 feet) • Bottom dwellers that live in crevices, bottles, etc • Have beak-like jaws and radula to rasp flesh and secrete paralyzing substance • Distract predators with dark fluid from ink sac

  27. Cephalopod: Squid • Squid • Two triangular fins on mantle – better swimmers than octopi • Can remain motionless, move forward, or backward • Eight arms and two tentacles, all with suckers • Has pen in upper surface of mantle • Few cm to 60 feet!!

  28. Cephalopod: Cuttlefish • Cuttlefish • Eight arms and two tentacles, but body flatten w/ fin running along the body • Have calcified internal shell aids in buoyancy

  29. Cephalopod: Chambered Nautilus • Chambered Nautilus • Coiled external shell containing gas filled chambers serves as buoyancy organ • Has suckerless tentacles

  30. Other Molluscs • Chitons (class Polyplacophora– bearer of many plates) • All marine • Eight overlapping shell plates covering dorsal surface • Live in shallow hard bottoms • Have radula to rasp algae

  31. Other Molluscs • Tusk shells or scaphopods (class Scaphopoda) • Elongated shell tapered at end resembling elephant tusk • Sandy muddy bottoms in deep water • Many species have thin tentacles to capture small prey Tusk shell hermit crab

  32. Biology of Molluscs: Nervous System • Gastropods and bivalves have ganglia (local brains) located in different parts of body

  33. Biology of Molluscs: Nervous System • Cephalopods • Most complex of invertebrates • Brains coordinate and store information • Complex eye reflects development • Octopi and cuttlefish can learn

  34. Biology of Molluscs: Nervous System • Cephalopods • Display rapid color change coordinated with behaviors and moods, from sexual display to camouflage • Cuttlefish “flash lights” while octopi change color and behavior to mimic poisonous fish and sea snakes http://www.sciencefriday.com/video/08/05/2011/where-s-the-octopus.html

  35. Biology of Molluscs: Reproduction and Life History • Most have separate sexes (some hermaphroditic) • Bivalves, chitons, tusk snails, and some gastropods release sperm and egg into water • Cephalopods and most gastropods – internal fertilization

  36. Biology of Molluscs: Reproduction and Life History • Cephalopods – modified arm to transfer spermatophore • Develop in yolk-filled eggs attached to crevices • Female dies – guarding eggs = no food • Some have trochophore larvae, displaying relationship to segmented worms

  37. Kings of Camouflage • http://www.youtube.com/watch?v=In7n590GjxU

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