The Animal Kingdom: The Protostomes

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