Phylum Mollusca Ch 12 – Molluscan Success

1. Phylum MolluscaCh 12 – Molluscan Success Mollusks are second only to arthropods in numbers of living species

2. Phylum Mollusca • Mollusca = “Soft Bodied” (Latin)

3. ~555 Million Years Ago

4. Molluscan Characteristics • Range in size and body shape • Largest  1000 lbs, 18m long (giant squid) • 80% less than 5 cm

5. Molluscan Characteristics • Body of three regions: head-foot, visceral mass, and mantle • Mantle cavity functions in excretion, gas exchange and reproduction • Bilateral symmetry • Protostome development • True coelomates (eucoelomates), reduced size • Open circulatory system in all but cephalopods • Radula present and used for scraping food

6. Mollusk Body • Three main regions • 1. Head-foot • Head (nervous structures) and foot (locomotion) • 2. Visceral Mass • Contain organs • 3. Mantle

7. Mollusk Body • Mantle • Usually attaches to the visceral mass and enfolds most of the body. May secrete the shell. • Mantle Cavity • Between the mantle and foot. Opens to the outside and functions in gas exchange, excretion and reproduction. • Radula • A rasping structure found in the mouth. “Toothed tongue”

8. Class Gastropoda • “Stomach foot” • Largest and most varied class of mollusks • ~35,000 living species • Examples: snails, slugs, conch, and limpets • Marine, freshwater, and terrestrial habitats

9. Class Gastropoda • Most have shells – calcium carbonate • Torsion - 180° twisting of the visceral mass, mantle, and mantle cavity. Used to bring head into shell. • Operculum closes shell opening. • Shell coiling: whorl, apex • Flattened foot for locomotion • Cilia • Muscular contractions • Use radula for scraping foot

10. Class Gastropoda Maintenance Functions • Gas exchange occurs in mantle cavity • Open circulatory system • 3 chambered heart • Hydraulic skeleton – fluid under pressure in body • Some dioecious, some monoecious

11. World’s Weirdest Gastropods • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-cone-snail/ • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/deadliest-zombie-snails/ • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-sea-hare/

12. Class Bivalvia • “Two valves” • Second largest molluscanclass: ~30,000 species • Includes clams, oysters, mussels, and scallops • Many edible, some form pearls

13. Bivalve Characteristics • Marine and freshwater • No head or radula • Most are filter feeders • Adductor muscles used for defense • Mantle attaches to shell around adductor muscles • Pearl forms when sand lands between mantle & adductor

14. Bivalve Characteristics • Foot projects from front end of animal, through the valves • Foot used for burrowing • Siphon – “neck” used for intake of water and food and release of waste. • Complete digestive tract • Reduced nervous system

15. Bivalve Shell and Shell Structures • Two convex halves of the shell – valves • Umbo – oldest part of shell near anterior end

16. Class Bivalvia Maintenance Function Reproduction • Cilia covered gills • Cillia move water in and out of mantle • Incurrent Pore • Excurrent Pore • Gills in mantle cavity for gas exchange • Food trapping – cilia move food toward mouth • Most are dioecious, some monoecious • Gonads in visceral mass • External fertilization (most) • Trocophore larvae

17. Beautiful Bivalves • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-clam-vs-world/ • https://www.youtube.com/watch?v=Z-32RfYNbOY

18. Class Cephalopoda • “Head Foot” • Includes octopuses, squid, cuttlefish, and nautiluses • Most complex mollusks/invertebrates • Foot modified into a circle of tentacles and a siphon • Shell reduced or absent in most • Head in line with elongate visceral mass

19. Cephalapod Shell • Shell reduced or absent in all but nautilus • Cuttlefish • Shell is internal. Cuttlebone is used to make polishing powder and bird treats (for calcium) • Squid • Pen: internal, chitinous structure • Cartilaginous plates in mantle wall, head, neck • Octopus • Absent

20. Class Cephalopoda Locomotion Maintenance Functions • Predators • Jet-propulsion system • Muscle contractions • Forces water out through narrow funnel • Cuttlefish and squid very motile • Octopus more sedentary • Adhesive cups used for capture. • Beaklike jaws and radula • Complete digestive tract • Closed circulatory system • Complex nervous system • Brain and Eye • Chromatophores for defense (color change) • Discharge of ink

21. Cephalopod Reproduction • Cephalopods are dioecious • One tentacle of male is modified for spermatophore transfer • Tentacles intertwine during copulation. Spermatophores burst open and eggs are released through the oviduct. • Fertilized eggs attach to substrate

22. World’s Weirdest Cephalopods • http://video.nationalgeographic.com/video/animals/invertebrates-animals/octopus-and-squid/deadliest-cuttlefish-camouflage/ • http://video.nationalgeographic.com/video/animals/invertebrates-animals/octopus-and-squid/octopus-vs-octopus-predation/ • http://dsc.discovery.com/tv-shows/other-shows/videos/is-it-possible-vampire-squid.htm

23. Class Polyplacophora • “many plates” • Chitons • Shallow marine waters • Reduced head, flattened foot • Shell dives into eight dorsal valves • Crawl similar to gastropods • http://www.youtube.com/watch?v=r1iEU2Kx7MI

24. Class Scaphopoda • “Boat foot” • Tooth shells or Tusk shells • Burrowing marine animals • Conical shell that is open at both ends • Head and foot project from wider end

25. Class Monoplacophora • “One plate” • Undivided, arched shell • Broad, flat foot • Repeated pairs of gills and foot-retractor muscles • Thought to be extinct until 1952

26. Class Aplacophora • “Without plate” • Lack a shell and crawl on ventral surface • Body and nervous system similar to flatworms • Most are surface dwellers on corals