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Chapter 18

0. Chapter 18. The Evolution of Animal Diversity. What Am I? Of some 1.5 million species of organisms known to science Over two-thirds are animals Humans have a long history of studying animal diversity But classifying an animal isn’t always easy.

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Chapter 18

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  1. 0 Chapter 18 The Evolution of Animal Diversity

  2. What Am I? • Of some 1.5 million species of organisms known to science • Over two-thirds are animals • Humans have a long history of studying animal diversity • But classifying an animal isn’t always easy

  3. Imagine you were the first person to encounter the animal pictured here • With all of its varying characteristics, what would you think it is?

  4. A Tasmanian tiger, 1928 • Biologists often encounter classification problems • When evolution creates organisms with similar characteristics

  5. Figure 18.1A What is an animal? • Animals are eukaryotic, multicellular heterotrophs • That ingest their food ANIMAL EVOLUTION AND DIVERSITY

  6. Animal development • May include a blastula, gastrula, and larval stage Key Haploid (n) Diploid (2n) Sperm 2 1 Egg Meiosis Zygote(fertilized egg) 3 Eight-cell stage Adult 8 Metamorphosis 4 Blastula(cross section) Digestive tract Ectoderm 5 Larva 7 Early gastrula(cross section) 6 Endoderm Futuremesoderm Figure 18.1B Internal sac Later gastrula(cross section)

  7. The ancestor of animals was probably a colonial, flagellated protist • Cells in these protists • Gradually became more specialized and layered Somaticcells Digestive cavity Reproductivecells 2Hollow sphere of unspecialized cells (shown in cross section) 3Beginning of cell specialization (cross section) 4Infolding (cross section) 1Colonial protist, an aggregate of identical cells 5Gastrula-like “proto-animal” (cross section) Figure 18.2A

  8. Figure 18.2B • Animal diversity exploded during the Cambrian period

  9. Top Dorsal surface Anterior end Posterior end Ventral surface Bottom Figure 18.3A Animals can be characterized by basic features of their “body plan” • Animal body plans may vary in symmetry

  10. Tissue-filled region (from mesoderm) Body covering (from ectoderm) Digestive tract (from endoderm) Body covering (from ectoderm) Muscle layer (from mesoderm) Digestive tract (from endoderm) Pseudocoelom Body covering (from ectoderm) Coelom Tissue layer lining coelomand suspendinginternal organs(from mesoderm) Digestive tract(from endoderm) • Vary in body cavity Figure 18.3B–D

  11. Development as either protostomes or deuterostomes • Together these animals show bilateral symmetry and three germ layers • Distinction between each is found in embryonic development

  12. Molluscs Annelids Sponges Flatworms Chordates Arthropods Cnidarians Nematodes Echinoderms Deuterostomes Protostomes Bilaterians Radial symmetry Bilateral symmetry Eumetazoans No true tissues True tissues Figure 18.4 Ancestral colonial protist The body plans of animals can be used to build phylogenetic trees • One hypothesis of animal phylogeny is based on morphological comparisons

  13. Invertebrates

  14. Figure 18.5A–C Sponges have a relatively simple, porous body • Sponges, phylum Porifera • Are the simplest animals and have no true tissues INVERTEBRATES

  15. Pores Choanocyte Amoebocyte Waterflow Skeletalfiber Centralcavity Flagella Choanocytein contactwith anamoebocyte Figure 18.5D • Flagellated choanocytes • Filter food from the water passing through the porous body

  16. Cnidarians are radial animals with tentacles and stinging cells • Cnidarians, phylum Cnidaria • Have true tissues and radial symmetry

  17. Figure 18.6A–C • Their two body forms are • Polyps, such as hydra • Medusae, the jellies

  18. Capsule(nematocyst) Coiledthread Tentacle “Trigger” Dischargeof thread Prey Cnidocyte Figure 18.6D • They have a gastrovascular cavity • And cnidocytes on tentacles that sting prey

  19. Flatworms are the simplest bilateral animals • Flatworms, phylum Platyhelminthes • Are bilateral animals with no body cavity

  20. Gastrovascularcavity Nerve cords Mouth Eyespots Nervoustissueclusters Figure 18.7A Bilateral symmetry • A planarian has a gastrovascular cavity • And a simple nervous system Planaria

  21. Units withreproductivestructures Scolex(anteriorend) HooksSucker Colorized SEM 80 • Flukes and tapeworms • Are parasitic flatworms with complex life cycles Figure 18.7B

  22. Nematodes have a pseudocoelom and a complete digestive tract • Nematodes, phylum Nematoda • Have a pseudocoelom and a complete digestive tract • Are covered by a protective cuticle

  23. Muscle tissue Trichinella juvenile Mouth Colorized SEM 400 LM 350 Figure18.8A, B • Many nematodes are free-living • And others are plant or animal parasites

  24. Visceral mass Reproductive organs Coelom Heart Kidney Digestive tract Mantle Shell Digestive tract Mantle cavity Radula Radula Anus Mouth Gill Mouth Foot Nerve cords Figure 18.9A Diverse molluscs are variations on a common body plan • All molluscs have a muscular foot and a mantle • Which may secrete a shell that encloses the visceral mass • Many mollusks • Feed with a rasping radula

  25. Figure 18.9B, C • Gastropods • Gastropods are the largest group of molluscs • And include the snails and slugs

  26. Figure 18.9D • Bivalves • The bivalves have shells divided into two halves • And include clams, oysters, mussels, and scallops

  27. Figure 18.9E, F • Cephalopods • Cephalopods are adapted to be agile predators • And include squids, cuttlefish and octopuses

  28. Annelids are segmented worms • The segmented bodies of phylum Annelida • Give them added mobility for swimming and burrowing

  29. Epidermis Anus Circular muscle Segment wall (partition between segments) Segment wall Longitudinal muscle Dorsal vessel Excretory organ Mucus-secreting organ Intestine Bristles Bristles Dorsal vessel Coelom Nerve cord Ventral vessel Excretory organ Digestive tract Brain Segment wall Blood vessels Giant Australian earthworm Mouth Nerve cord Pumping segmental vessels • Earthworms and Their Relatives • Earthworms • Eat their way through soil • Have a closed circulatory system Figure 18.10A

  30. Figure 18.10B, C • Polychaetes • Form the largest group of annelids • Search for prey on the seafloor or live in tubes and filter food particles

  31. Figurer 18.10D • Leeches • Most leeches • Are free-living carnivores, but some suck blood

  32. Cephalothorax Abdomen Thorax Antennae (sensory reception) Head Swimming appendages Walking legs Figure 18.11A Mouthparts (feeding) Pincer (defense) Arthropods are segmented animals with jointed appendages and an exoskeleton • The diversity and success of arthropods is largely related to their segmentation, exoskeleton, and jointed appendages

  33. Colorized SEM 900 A black widow spider (about 1 cm wide) A dust mite (about 420 µm long) A scorpion (about 8 cm long) Figure 18.11B, C • Chelicerates • Chelicerates include • Horseshoe crabs • Arachnids, such as spiders, scorpions, mites, and ticks

  34. Figure 18.11D • Millipedes and Centipedes • Millipedes and centipedes • Are identified by the number of jointed legs per body segment

  35. Figure 18.11E • Crustaceans • The crustaceans • Are nearly all aquatic • Include crabs, shrimps, and barnacles

  36. Insects are the most diverse group of organisms • Insects have a three-part body consisting of • Head, thorax, and abdomen • Three sets of legs • Wings (most, but not all insects)

  37. Many insects undergo • Incomplete or complete metamorphosis

  38. Abdomen Head Thorax Antenna Forewing Eye Mouthparts Hindwing • A. Order Orthoptera • The order orthoptera includes • Grasshoppers, crickets, katydids, and locusts Figure 18.12A

  39. Figure 18.12B • B. Order Odonata • The order odonata includes • Dragonflies and damselflies

  40. Figure 18.12C • C. Order Hemiptera • The order hemiptera includes • Bedbugs, plant bugs, stinkbugs, and water striders

  41. Figure 18.12D • D. Order Coleoptera • The order coleoptera includes • Beetles

  42. Figure 18.12E • E. Order Lepidoptera • The order lepidoptera includes • Moths and butter flies

  43. Haltere Figure 18.12F • F. Order Diptera • The order Diptera includes • Flies, fruit flies, houseflies, gnats, and mosquitoes

  44. Figure 18.12G • G. Order Hymenoptera • The order hymenoptera includes • Ants, bees, and wasps

  45. Tube foot Echinoderms have spiny skin, an endoskeleton, and a water vascular system for movement • Echinoderms, phylum Echinodermata • Includes organisms such as sea stars and sea urchins • Are radially symmetrical as adults Tube foot Spine Figure 18.13B, C

  46. Anus Spines Stomach Tube feet Canals Figure 18.13A • The water vascular system • Has suction cup–like tube feet used for respiration and locomotion

  47. Our own phylum, Chordata, is distinguished by four features:

  48. Excurrent siphon Post-anal tail Dorsal, hollow nerve cord Head Pharyngeal slits Notochord Mouth Mouth Muscle segments Pharynx Dorsal, hollow nerve cord Pharyngeal slits Notochord Digestive tract Water exit Post-anal tail Adult (about 3 cm high) Larva Segmental muscles Anus Figure 18.14A, B • The simplest chordates are tunicates and lancelets • Marine invertebrates that use their pharyngeal slits for suspension feeding

  49. Chordates Craniates Vertebrates Jawed vertebrates Tetrapods Amniotes Lobe-fins Reptiles Lancelets Mammals Hagfishes Tunicates Lampreys Amphibians Milk Sharks, rays Ray-finned fishes Amniotic egg Legs Lobed fins Lungs or lung derivatives Jaws Vertebral column Head Brain Ancestral chordate Derived characters define the major clades of chordates • A chordate phylogenetic tree • Is based on a sequence of derived characters VERTEBRATES Figure 18.15

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