Mollusks and Annelids

1. Mollusks and Annelids Chapter 23+

2. Annelids and Mollusks • Coelomates • Trochophore larvae • Bilateral symmetry • More complex organ systems

3. Moving On Up

4. Coelom • Coelomates • Evolutionary milestone • True body cavity • Forms within mesoderm • Internal body organs cushioned by fluids in cavity

5. Trochophore Larva • Larval stage • Most Mollusks and Annelids • Suggests related? • Develops from fertilized egg • Ciliated • In some species free-swimming

6. The Mollusks • Second largest animal phylum • Widespread • More species of terrestrial mollusks than all terrestrial vertebrates • 7 classes

7. Mollusk Characteristics • Body cavity • True coelom • Small area around heart • Bilateral symmetry • Three part body plan • Foot • Muscular • Locomotion • Visceral mass • Contains organs • Mantle • Fold of tissue • Outer layer of body • Cape-like

8. Characteristics- Continued • More organ systems • Excretion, circulation, respiration, digestion, and reproduction • Shell • Many mollusks • One or two • Protein + CaCO3 • Protection • Radula • All, except bivalves • Tongue-like • Rasping • Feeding

9. Mollusk Classification • Domain = Eukarya • Kingdom = Animalia • Phylum = Molluska • Three major classes: • Gastropoda • Bivalvia • Cephalopoda • Nemo Mollusk joke 1:15

10. Mollusks • Only coelomates w/out segmented body

11. Mollusk Digestion • Complete digestive system • One-way • Two openings • Varies in mollusk groups • More complex than roundworms

12. Mollusk Excretion • Removal of metabolic wastes • Wastes in body fluids collect in coelom • Fluid pulled into nephridia by cilia • Tiny tubes • Recover water, sugars, and salts

13. Excretion • Useful molecules reabsorbed • Waste fluid leaves through pore in mantle cavity • All coelomates have nephridia except • Arthropods • Chordates

14. Mollusk Circulation • Circulatory system! • Diffusion won’t work • Most: • 3 chambered heart • Open system • Blood sloshes in hemocoel • Exception: • Octopi and squid

15. Mollusk Respiration • Most have gills: • In mantle cavity • Cilia beat and move water • Gills extract >50% of dissolved O2

16. Mollusk Respiration • Terrestrial snails • Membrane lines mantle cavity • Primitive lung • Must be moist • Active at night and after rain • Sea snails • No gills • Gas exchange thru skin

17. Mollusk Reproduction • Most = distinct sexes • Some snails and slugs are hermaphrodites • Some sea slugs and oysters can change back and forth between sexes!

18. Reproduction • Larval forms • Many marine mollusks have trochophore • Ciliated and moves • Squid, octopi, and freshwater snails and some freshwater mussels • No free swimming larva • Larva form within egg

19. Just to really keep your interest! • Celtic Mollusk presentation 3:30

20. Gastropods

21. Gastropods • Largest mollusk class • 40,000 species • Snails, nudibranches, and slugs • Single or no shell

22. Gastropoda • Muscular foot -locomotion • Mostly marine • Size • Microscopic to 1 meter • Nudibranch clip - 27 sec

23. Gastropod Feeding Habits • Some herbivores • Radula • Scrape algae off rocks • Some are predators • Radula • Drill into other mollusks • Ex: Cone shell • Uses poison • Swallow prey

24. Gastropods and Humans • Can be pests • Garden and agricultural • Can be eaten • Genus Helix raised on snail farms • Conchs are considered delicacies

25. Bivalvia

26. Bivalves • All aquatic • Most marine • Two hinged shells • Secreted by mantle • Ligaments and muscles hold shells together • Adductor muscles

27. Bivalves • Head is reduced • Radula absent • Most are filter feeders • Most are sessile

28. Bivalve Nervous System • Nerve ganglion • Simple brain • Simple sense organs • Sense organs on edge of mantle • Sensitive to light and touch • Giant Clam 6:47

29. Bivalve Reproductive System • Most have distinct sexes • Few hermaphrodites • Reproduce sexually • Release gametes into water

30. Bivalve Reproductive System • Fertilized egg develops into free swimming trochophore larva • Few brooded in pouches • Then complete life cycle as parasite on fish gills

31. Bivalve Filter Feeding • Slow moving creatures • Cilia on gills • Create water flow • Siphons • Hollow tubes • Inlet and outlet • Gills • Mucus covered • Trap microorganisms • Cilia move mucus to mouth

32. Bivalve and Humans • Human food resource • Oysters, clams, scallops, mussels • Over 6.5 billion lbs/yr • Demand increasing

33. Bivalve and Pearls • Many bivalves produce pearls: • Foreign object trapped between shell and mantle • Coat irritant with sheets of nacre • Mother-of –pearl • Like the inner layer of shell

34. Bivalve and Pearls • Only a few species • Gem-quality pearls • Pearls • Thin sheets of nacre • Over-lapping mineral crystals • Act-like prisms • Makes pearls iridescent • Cultured pearls

35. Clam Structure

36. Clam Structure

37. Cephalopods

38. Cephalopods • Shell is reduced or absent • Nautilus is the only living cephalopod with an external shell • Small internal shell of cuttlefish • Bird cages for calcium • Active marine predators • Closed circulatory system • Beak-like jaws • Large head • Foot divided into tentacles • Suckers or hooks

39. Shark vs Octopus showdown

40. Cephalopods • Most advanced group of mollusks • Most intelligent of all invertebrates • Complex nervous system • Well developed brain • Eye structure similar to vertebrate eye • Exhibit complex behaviors • Cephalopod character 3:40

41. Cephalopod Movement • “Jet propelled” • Draw water into mantle cavity • When threatened • Close mantle cavity quickly • Force water out of siphon

42. Cephalopod Escape • Squids and octopuses • Release dark fluid • Clouds water • Confuses predators • Conceals escape route • Cuttlefish ink • Sepia • Used by artists • Many famous paintings • Cephalopod Defense 2:30

43. Cephalopod Feeding • Marine predators • Eat • Fish • Crustaceans • Worms • Use: • Tentacles • Beak-like jaws • Radula pulls in food • Feeding video 2 min

44. Moving On Up

45. The Segmented Worms • Phylum annelida • Anellus • Latin - “Little rings” • Segmented bodies • Also known as metamerism • All coelomate animals except mollusks • Evolutionary milestone

46. Body Segments • Series of ring-like structures • Each segment contains organs: • Digestive, excretory, circulatory, muscular • Some segments modified • Special function: • Reproduction, feeding, sensation • Septa • Internal body walls that separate segments

47. General Characteristics • 1) Coelom • Larger than mollusks • 2) Most have bristles • Setae- external bristles • Parapodia - fleshy appendages • 3) Organ Systems • Highly specialized • Closed circulatory system • Nephridia • Digestive system • Primitive brain = cerebral ganglion

48. Annelid Classification • Domain Eukarya • Kingdom Animalia • Phylum Annelida • Classes: • 1) Polychaeta • 2) Oligochaeta • 3) Hirudinea • Differ in # of setae/segment • Presence/absence of parapodia

49. Class Polychaeta • Poly = “many” • Chaeta = “seta” • Marine worms • Largest group of annelids • Live in all oceans • Often have setae Feather duster worm

50. Class Polychaeta • Unusual forms and colors • Pair of parapodia on most segments • Swim, crawl, burrow • Increase surface area • Gas exchange