1. Mollusca and Annelida

2. Relationship of Mollusca and Annelida  Similar patterns of embryology  True coelom  Fluid filled cavity within the mesoderm

3. Advantages of a Coelom  Digestion independent of locomotion  Circulatory system functions without interference from other organs  Hydrostatic skeleton against which the muscles can contract

4. Trochophore Larvae  Larval Similarities between Annelids and Mollusks  Pear shaped ciliated larvae  Cilia on both ends and middle  Dispersal of offspring  Advantage for shell burdened adults  Terrestrial forms develop within the egg; Not free-living

5. Importance of Mollusks  100,000 species  Some are filter feeders  Others are active predators  Some are alternative parasitic hosts  Some cause considerable economic damage to crops  Others are valued by collectors

6. Characteristics  True coelom  Distinct parts  Muscular foot  Head  Visceral mass  Bilateral symmetry  One or more shells in most species

7. Organ Systems  Respiratory  Digestive  Circulatory  Excretory  Nervous  Reproduction

8. Body Plan  Muscular foot for locomotion  Head contains mouth, sense organs and central ganglia  Visceral mass containing heart, digestive, excretory, and reproductive organs

9. Mantle  Epidermal layer secretes shell  Covers visceral mass

10. Shell  Calcium carbonate shells evolved early  Adaptation to protect soft body from predation  Reduces surface area for gas exchange

11. Gill  Large surface area  Rich supply of blood  Specialized for gas exchange  Protected within mantle cavity  Between mantle and visceral mass

12. Class Polyplacophora  Chitons  Shells divided into 8 overlapping plates

13. Class Gastropoda  75,000 species  Snails, slugs, abalones, nudibranchs, and conches  Single shell (valve) or none

14. Body Plan  Based on ancestral mollusks  Torsion results from twisting during larval development  Visceral mass twists 180 degrees in relation to the head  Mantle cavity in front of animal  Allows head to be drawn into mantle cavity

15. Snails  Wide variety of habitats  Terrestrial  Aquatic (freshwater and marine)

16. Respiration - Aquatic Snails  Respire through gills in mantle cavity

17. Respiration - Terrestrial Snails  Mantle cavity acts as modified lung  Allows gas exchange with air  Membrane must be keep moist to allow gas exchange  Retreats into shell and seals opening with mucus in dry environment

18. Circulation  Open circulatory system  Blood does not circulate entirely within vessels  Collected from gills (lungs) and pumped through heart  Released directly into spaces in the tissue (hemocoel)  Returned via gills or lungs to heart

19. Digestion  Saw like radula with flexible tongue like strip covered with chitinous teeth  Scrape up algae (aquatic)  Saw off leaves

20. Reproduction  Land snails hermaphroditic  Most aquatic species have distinct sexes  Internal fertilization

21. Movement  Muscular contractions of the foot  Glands in foot secrete layer of mucus

22. Sensory  2 eyes on retractable tentacles

23. Other Gastropods Slugs  Lack shells  Moist environment Oyster Drills  Drill like radula

24. Bivalvia  Clams, oysters, scallops, and shipworms  Sessile  Filter feeders  2 valves (shells)  Muscular foot  Lack distinct head region  Anterior ganglia

25. Shell 3 layers secreted by mantle Thin outer layer  Protects shell against acidic conditions Thick middle layer  Composed of calcium carbonate crystals  Strengthens shell Smooth inner layer  Protects animals soft body

26.  Mantle secretes mother of pearl  Hinge connects the two valves  Powerful adductor muscles

27. Clams  Adapted for filter feeding  Beating cilia on gills setup current  Water enters incurrent siphon  Propelled over gills  Exit through excurrent siphon

28. Digestion  Food trapped in sticky mucus  Cilia moves mucus into mouth

29. Respiration  Water passes over gills  Oxygen diffuses into blood  Carbon dioxide diffuses out

30. Nervous  Cells along edge of mantle respond to light and touch  Ganglia located above mouth, in the digestive system, and foot  Connected by 2 pairs of long nerve cords

31. Reproduction  Separate sexes  Shed sperm and eggs into water  External fertilization  Zygote -> trochophore larvae  Larvae settles to bottom -> adult

32. Other Bivalves  Oysters  Permanently attached to substrate  Scallops move by jet propulsion  Teredo (shipworm) bores into driftwood  Symbiotic protozoa that digests cellulose

33. Cephalopoda  Octopuses, squids, cuttlefish, and chambered nautiluses  Well developed head  Prominent foot divided into tentacles  Free swimming  Predatory  Strong suckers  Radula and sharp beak

34.  Closed circulatory system  Blood circulates entirely within blood vessels  Allows for high metabolic rate

35. Squids  Marine  Largest invertebrate (20 M; 3,360 kg)  Large complex brain  Highly developed nervous system  Large pair of vertebrate like eyes

36.  Ten tentacles  Largest pair used to capture prey  Smaller pairs force prey into mouth  Muscular mantel propels by pumping water through siphon  Excrete inky substance when threatened

37.  Chromatophores - change color  Internal fertilization  Lay mass of gelatinous encased eggs  Maternal protection until hatching

38. Octopus  Eight tentacles  Similar to squids  Scrawl along bottom looking for prey

39. Chambered Nautilus  Retain exterior shell  Lives in outer chamber of its shell  Secretes gas into other chamber  Regulates buoyancy

40. Annelida  Segmented worms  Feather worms, earthworms, and leeches  True coelom  Body divided into segments (metamerism)

41.  Some segments fused  Well developed organ system  Most have external bristles (setae)

42. Classification  Based on number of setae and presence or absence of parapodia (fleshy appendages)

43.  Class Oligochaeta  No parapodia and few setae  Class Hirudinea  No setae or parapodia  Class Polychaeta  Many setae and parapodia

44. Class Oligochaeta  Earthworms

45. Structure  More than 100 segments  Segments separated by partitions that divide coelom  Segments identical except when specialized and fussed  Anterior and posterior ends

46.  Cephalization specialized for burrowing  Head contains sense organs  Circular and longitudinal muscles

47. Movement  Setae anchored during movement  Circular muscles contract  Hydrostatic pressure increases in anterior coelomic cavities

48.  Body elongates pushing head forward  Anterior setae grip ground  Longitudinal muscles contract  Posterior pulled along  Coelomic divisions allow simultaneous contraction and expansion of segments

49. Feeding  Feed on organic matter in soil  Digest organic matter  Wastes and undigested soil eliminated as casting  Loosens and aerates soil

50. Digestion  Soil sucked in by pharynx ->  Esophagus ->  Crop (storage) ->  Gizzard (grinds soil releasing organic matter) -> Intestines (nutrients absorbed)  Intestines (nutrients absorbed)

51. Circulation  Transport oxygen, nutrients, and wastes  Flow of blood toward posterior via ventral blood vessel  Flow of blood toward anterior via dorsal blood vessel

52.  5 pair of aortic arches link vessels near anterior  Smaller vessels branch into segments  Contraction of ventral vessel and aortic arches forces blood through body

53. Respiration  Lack respiratory organs  Oxygen and carbon dioxide diffuse across skin  Requires moist skin  Limited habitat  Secrete mucus  Thin cuticle

54. Excretion  Elimination of nitrogen wastes  Long tubules (nephridia) excrete wastes  Coelomic fluid enters nephridium through ciliated funnel opening  Some water reabsorbed by blood  Remaining fluid excreted through ventral pores

55. Nervous  Sensitive to touch, light, moisture, chemicals, temperature, and vibrations  Light receptors on head and tail  Sense direction Anterior Ganglia Ventral Nerve cord

56.  Most other sense organs and nerves that control muscle contractions found in individual segments  Pair of ganglia in each segment coordinate movement with adjacent segments  Cerebral ganglion in head  Controls total body  Ventral nerve cord connects brain with ganglia

57. Reproduction  Hermaphrodites  Cannot self fertilize  Worms join head to tail  Form mucus coat around bodies  Each inject sperm into mucus

58.  Sperm move to seminal receptacle  Eggs move through oviducts to female genital pore  Clitellum secretes mucus and chitinous sheath  Worm wiggles to slip off sheath  Eggs and sperm join

59. Class Polychaeta  Polychaetes  Marine  Some free swimming predators with strong jaws  Some burrowing

60.  Numerous setae projecting from parapodia used for movement  Some parapodia function in respiration  Have antennae and specialized mouth parts

61. Hirudinea  Leeches  No setae  Anterior and posterior sucker (walking motion)  Fresh water