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The Animal Kingdom: The Protostomes

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  1. The Animal Kingdom:The Protostomes Chapter 30

  2. Learning Objective 1 • Cite specific examples of the evolutionary significance of the coelom

  3. Coelom 1 • True coelom is a fluid-filled body cavity • completely lined by mesoderm between digestive tube and outer body wall • Allows tube-within-a-tubebody plan • body wall is outer tube • inner tube is digestive tube

  4. Coelom 2 • An enclosed compartment (or series of compartments) of fluid under pressure • Serve as hydrostatic skeleton • contracting muscles push against tube of fluid

  5. Coelom 3 • A space in which internal organs develop • including gonads • Helps transport materials • Protects internal organs

  6. KEY CONCEPTS • Evolution of the coelom has been associated with important innovations in body plan, including cephalization, the tube-within-a-tube body plan, compartmentalization, and segmentation

  7. Learning Objective 2 • Characterize the protostomes • Describe their two main evolutionary branches • Give examples of animals assigned to each branch

  8. Protostomes • Characterized by • spiral cleavage • determinate cleavage • development of mouth from blastopore

  9. Two Branches of Protostomes • Lophotrochozoa • platyhelminths, nemerteans, mollusks, annelids, lophophorate phyla, rotifers • Ecdysozoa • nematodes (roundworms) and arthropods

  10. KEY CONCEPTS • Protostomes are a monophyletic group that gave rise to two major clades: Lophotrochozoa and Ecdysozoa

  11. Learning Objective 3 • What are the distinguishing characteristics of phylum Nemertea and phylum Platyhelminthes? • Describe the main classes of phylum Platyhelminthes, giving examples of animals that belong to each class

  12. Phylum Nemertea (Ribbon Worms) 1 • Characterized by proboscis • muscular tube for capturing food, defense • Reduced coelom (rhynchocoel) • space surrounding proboscis

  13. Phylum Nemertea (Ribbon Worms) 2 • Nemerteans have • tube-within-a-tube body plan • complete digestive tract with mouth and anus • a circulatory system

  14. Nemerteans

  15. Phylum Platyhelminthes (Flatworms)1 • Acoelomate animals with • bilateral symmetry • cephalization • 3 definite tissue layers • well-developed organs • Many are hermaphrodites • single animal produces both sperm and eggs

  16. Phylum Platyhelminthes (Flatworms)2 • Ladder-type nervous system • sense organs • simple brain composed of two ganglia • 2 nerve cords that extend the length of body • Protonephridia • function in osmoregulation and disposal of metabolic wastes

  17. 3 Classes ofPhylum Platyhelminthes • Class Turbellaria • free-living flatworms, including planarians • Classes Trematoda and Monogenea • parasitic flukes • Class Cestoda • parasitic tapeworms

  18. Planarian

  19. Lophotrochozoa Lophophorate phyla Platyhelminthes Deuterostomia Ecdysozoa Nemertea Mollusca Annelida Parazoa Rotifera Radiata Choanoflagellate ancestor Fig. 30-1 (1), p. 642

  20. Ganglia Auricle Auricle Eyespot Nerve Gastrovascular cavity Pharynx Sheath surrounding pharynx Mouth 1 mm Fig. 30-1ab, p. 642

  21. Pharyngeal sheath cavity Inner muscle layer of pharynx Pharyngeal cavity Outer muscle layer Muscle Epidermis Adhesive gland Sperm mass Ventral nerve cords Cilia Body wall composed of epidermis, circular muscle, and longitudinal muscle Muscle layers Fig. 30-1c, p. 642

  22. Insert “Planarian organ systems” planarian_organs_v2.swf

  23. Parasitic Flukes and Tapeworms • Typically have suckers or hooks • for holding on to their hosts • Have complicated life cycles • intermediate hosts • large numbers of eggs

  24. Parasitic Fluke

  25. Larvae make their way to circulatory system, where they mature. During reproduction, which takes place in veins, male holds female in a long groove. 2 1 Larvae burrow through skin. 1 mm 3 Eggs pass into intestine. 7 Finally, fork-tailed larvae (cercariae) develop and leave snail. 4 Eggs containing developing embryos are excreted with feces. 6 Larvae must enter a second host, a freshwater snail. After burrowing into tissues of snail, larvae develop into a form that reproduces asexually. 5 If they find their way to fresh water, the eggs hatch, releasing free-swimming larvae (miracidia). Fig. 30-2, p. 644

  26. Tapeworm

  27. Insert “Blood fluke life-cycle” and “Tapeworm life cycle” blood_fluke.swf tapeworm.swf

  28. Watch the fluke and tapeworm life cycles by clicking on the figures in ThomsonNOW.

  29. Learning Objective 4 • What are the adaptive advantages of cephalization?

  30. Cephalization • Evolution of a head • concentration of sense organs and nerve cells (simple brain) at anterior end • (Flatworms show beginnings of cephalization) • Increases effectiveness of bilateral animal • to actively find food, shelter, mates • to detect enemies

  31. Learning Objective 5 • What are the distinguishing characteristics of phylum Mollusca and the four molluscan classes discussed? • Give examples

  32. PhylumMollusca • Soft-bodied animals • usually covered by a shell • Ventral foot • for locomotion • Mantle • covers visceral mass (body organs)

  33. Mollusks • Most have open circulatory system • Cephalopods have closed circulatory system • Most have rasplike radula for feeding • Bivalves are suspension feeders • Most marine mollusks have free-swimming, ciliated trochophore larva

  34. Insert “Molluscan classes” mollusk_classes.swf

  35. Trochophore Larva

  36. Digestive tract Cilia Mouth Nephridium Mesodermal cells Anus Fig. 30-7, p. 648

  37. ClassPolyplacophora • Includes marine chitons • Shells consist of 8 overlapping plates

  38. Shell Digestive tract Class Polyplacophora Fig. 30-6a, p. 647

  39. ClassGastropoda • Largest group of mollusks • snails, slugs, and their relatives • Body undergoes torsion • a twisting of the visceral mass

  40. Shell Digestive tract Foot Class Gastropoda Fig. 30-6b, p. 647

  41. Insert “Snail body plan” snail_body_plan.swf

  42. Torsion

  43. Insert “Torsion in gastropods” torsion.swf

  44. ClassBivalvia • Includes aquatic clams, scallops, oysters • Two-part shell • hinged dorsally • encloses bodies • Suspension feeders

  45. Shell Digestive tract Foot Class Bivalva Fig. 30-6c, p. 647

  46. Clam

  47. Heart Digestive gland DORSAL Metanephridium Stomach Intestine Esophagus Posterior adductor muscle Ganglion Anus Anterior adductor muscle Excurrent siphon Mouth Incurrent siphon Palp Gill—partially cut Pedal ganglion Mantle Foot Shell Intestine Gonad VENTRAL Fig. 30-10, p. 649

  48. Insert “Clam body plan” clam.swf

  49. ClassCephalopoda • Includes squids, octopods, Nautilus • Active, predatory swimmers • Tentacles surround the mouth • located in the large head

  50. Tentacles (modified foot) Internal shell Digestive tract Class Cephalopoda Fig. 30-6d, p. 647