1. Molluscs Most Complex of the Invertebrates

2. Molluscan Success Most closely related to Annelids ( segmented worms) based on protostome characteristics Have a coelom, are triploblastic Have declined dramatically with the rise of vertebrates, Currently 100,000 living species Subkingdom Lophotrochozoan along with annelids due to Larva (trochopore) and feeding structure

3. Molluscan Characteristics Bilateral symmetry, two part body: Head- foot and Visceral Hump Mantle- tissue surrounding visceral mass, secretes calcerous shell Mantle cavity performs excretion, gas exchange, elimination, and reproductive cells Open circulatory system in all but one class (Cephalopoda ) Coelom surrounding heart and gonads

4. Molluscan Shell Structure Shell secreted by Mantle, 3 Layers: Periostracum- outer layer, rough, Protein Prismatic- middle layer, thickest, calcium carbonate and organic material Nacreous Layer- inner layer, thin sheets, calcium carbonate alternating with organic matter, Pearly layer Some Molluscs have lost shell entirely or severely reduced

6. Gastropods (Stomach Footed) Largest Class of Molluscs, Includes snails, limpets (Univalves) and slugs( Nudibranchs) Marine, freshwater and Terrestrial varieties Torsion of Body 180 degrees in shell- Positions gills, visceral mass and Anus just behind head With torsion the head enters the shell first, foot last, covered by operculum (calcareous) Digestive Tract U shaped, notches in shell allow wastes to escape

10. Gastropoda Structure Shell Coiling- Asymmetrical in most modern snails, each successive coil larger than and ventral to the preceding coil, compact shell Flattened foot, ciliated with gland cells, larger snails use muscular contractions to move Modified foot in some for clinging (abalones, Limpets) or for swimming (Sea Hares)

11. Subclass Opisthbranchia Includes Sea Hares, Sea Slugs etc. Shell, mantle cavity and gills are reduced or lost, if gills are present located on dorsal surface, may have nematocysts, warning coloration Many acquire undischarged nematocysts from cnidaria they eat, Glaucus open ocean swimming snail eats man-of-war Pterapods have a foot modified for swimming, large food source in cold water

16. Gastropoda Feeding Radula- Rasping structure chitinous belt with hooked teeth, muscles pull radula over a cartilage structure which can be extended from mouth. Most feed by scraping Algae or small organisms from substrate (deposit feeders), some herbivores, scavengers, parasites and predators Trap food on mucus strings which extend into stomach, rotated by cilia, digestion by enzymes

19. RADULA

20. Gastropod Anatomy Carnivorous species have modified radula into a hollow Harpoon for injecting Tetrodoxin poison( causes respiratory paralysis) Cone snails Siphon- a rolled extension of the mantle, extends out of shell, brings in water Open circulatory system with 2 chambered Heart, Blood leaves blood vessels directly bathes tissues in sinuses

22. QUEEN CONCH

23. Gastropod Nervous System Concentration of ganglia in Head Eyes may be simple photoreceptors or may contain a Lens and Cornea, Stalked Statocysts- balance organs Osphridia- Chemoreceptors anterior wall of mantle cavity, Smell

24. Gastropod Reproduction Many are Dioecious, discharge gametes into sea, external fertilization Some Monoecious, internal cross fertilization is the rule, some Protandric where testes develop first and degenerate, ovaries develop later Trochophore Larva- free swimming Veliger Larva- free swimming with foot, eyes, shell, settle on bottom undergo metamorphosis

25. TROCHOPHORE

27. Bivalve Class Second largest Molluscan class, includes Clams, Oysters, mussels and scallops Two convex halves to shell (valves), some produce pearls Dorsal margin has proteinaceous hinge Teeth- tongue and groove modifications to shell keep it from twisting Most Filter feeders, Sedentary, clean bacteria from water

31. Bivalve Anatomy Loss of Head and Radula, Expansion of cilia covered gills, Folded ( increase surface area) Water enters mantle cavity thru incurrent siphon, movement of cilia does pumping, water circulates thru water tubes in gills exchange O2 and CO2 with blood, exits thru excurrent opening in mantle Food is trapped by the gills and carried to the mouth by cilia who sort thru it, expell particles too large

32. Cephalopoda (head footed) Includes octopus, squid, cuttlefish and nautilus Anterior portion of foot modified into tentacles or arms used for capturing prey, attachment, locomotion and copulation Foot incorporated into a funnel attached to the highly muscular mantle cavity used for jetting locomotion Head in line with the visceral hump

34. Shell Nautilus is the only member with an external shell, last chamber only one occupied the rest are gas filled, control bouyancy Cuttle fish- internal cuttle bone, made of thin layers Squid- internal chitinous structure called a pen, two long thin rods, also have cartilage plates in the head, mantle wall, and neck for protection and support

35. Locomotion Mantle contains radial and circular muscles, radial bring water in, circular expels it Muscles attached to siphon control direction of animals movement Posterior fins aid in steering, propulsion and stabilization Octopus normally crawl over bottom, jet to escape predators

36. Feeding and Digestion Excellent Vision, vertebrate like eye, locates prey, captured by tentacles or extensible arms Tentacles equipped with suction cups, some have edge reinforced with tough protein and hooks Mouth has jaws and a radula, Jaws are beak shaped and radula rasps food into mouth Octopus have salivary glands that inject venom

39. SQUID BEAK

44. Cephalopod Anatomy Closed circulatory System with arteries, veins and capillaries, 3 chambered heart Brachial hearts at the base of each gill Nephridia collect wastes directly from blood Complex nervous system, statocyst, chemoreceptors Chromatophores and irridophores change color of body, camoflage, warning coloration

45. Class Polyplacophora Chitons- have a reduced head, flattened foot and a shell divided into 8 segments (valves) Muscular mantle extends beyond shell covers foot Muscular foot creates suction holds animal tight to rocks, if dislodged rolls into ball Feed on attached algae with radula Body Indicates early ancestral segmentation

46. CHITON