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CHAPTER 25 The Development of the Animal Kingdom Honors Biology.

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1 CHAPTER 25 The Development of the Animal Kingdom Honors Biology

2 Animals –Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion –Digest their food within their bodies What Is an Animal? Figure 17.2

3 Most animals reproduce sexually and then proceed through a series of developmental stages Most animals have muscle cells and nerve cells that control the muscles Figure 17.3 Egg Sperm Fertilization Zygote (fertilized egg) Blastula (cross section) Early gastrula Later gastrula Outer cell layer (ectoderm) Opening Primitive gut Inner cell layer (endoderm) Larva Digestive tract Metamorphosis Adult Meiosis Haploid Diploid

4 Early Animals and the Cambrian Explosion Animals probably evolved from a colonial protist that lived in the Precambrian seas Figure 17.4 Reproductive cells Somatic cells Digestive cavity Early colony of protists (aggregate of identical cells) Hollow sphere (shown in cross section) Beginning of cell specialization 5 Gastrula-like “proto- animal” Infolding

5 At the beginning of the Cambrian period, 545 million years ago, animals underwent a rapid diversification Figure 17.5

6 To reconstruct the evolutionary history of animal phyla, researchers must depend on clues from comparative anatomy and embryology Four key evolutionary branch points have been hypothesized –The first branch point is defined by the presence of true tissues Animal Phylogeny

7 Multicellularity True tissues Radial symmetry Bilateral symmetry No body cavity Body cavities Pseudocoelom True coelom Coelom from cell masses Coelom from digestive tube Figure SpongesCnidarians Flatworms Roundworms Mollusks Annelids Arthropods Echinoderms Chordates

8 –The second major evolutionary split is based partly on body symmetry Figure 17.7 (a) Radial symmetry (b) Bilateral symmetry

9 –Third, the evolution of body cavities led to more complex animals A body cavity Is a fluid-filled space separating the digestive tract from the outer body wall May be a pseudocoelom or a true coelom Figure 17.8 (a) No body cavity (e.g., flatworm) Body covering (from ectoderm) Digestive tract (from endoderm) Tissue-filled region (from mesoderm) (b) Pseudocoelom (e.g., roundworm) Pseudocoelom Digestive tract (from endoderm) Body covering (from ectoderm) Muscle layer (from mesoderm) (c) True coelom (e.g., annelid) Coelom Digestive tract (from endoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Mesentery

10 –Fourth, among animals with a true coelom, there are two main evolutionary branches, which differ in embryonic development

11 Divided into invertebrates and vertebrates –Invertebrates are animals without backbones Represent 95% of the animal kingdom THE KINGDOM ANIMALIA

12 Phylum Porifera –Includes sessile animals once believed to be plants –Lack true tissues The body of a sponge resembles a sac perforated with holes –Draws water into a central cavity, where food is collected Invertebrates - Sponges Figure 17.9

13 Figure Pores Water flow Skeleton fiber Central cavity Choanocyte Amoebocyte Choanocyte in contact with an amoebocyte Flagella

14 Invertebrates - Cnidarians Phylum Cnidaria –Is characterized by organisms with radial symmetry and tentacles with stinging cells

15 The basic body plan of a cnidarian –Is a sac with a gastrovascular cavity –Has two variations: the sessile polyp and the floating medusa Mouth/anus Tentacle Gastrovascular cavity Tentacle Mouth/anus Medusa form Polyp form Figure 17.11

16 Examples of polyps are –Hydras, sea anemones, and coral animals Figure 17.12

17 The organisms we call jellies are medusas

18 Cnidarians are carnivores that use tentacles armed with cnidocytes, or “stinging cells,” to capture prey Figure Tentacle Coiled thread Capsule “Trigger” Discharge of thread Cnidocyte Prey

19 Phylum Platyhelminthes –Is represented by the simplest bilateral animals –Includes free-living forms such as planarians Invertebrates - Flatworms Figure Digestive tract (gastrovascular cavity) Nerve cords Mouth Eyespots Nervous tissue clusters

20 Some flatworms are parasitic –Blood flukes are an example –Tapeworms parasitize many vertebrates, including humans Figure Reproductive structures Head Hooks Sucker

21 Phylum Nematoda –Includes the most diverse and widespread of all animals –Occurs in aquatic and moist terrestrial habitats Invertebrates - Roundworms Figure 17.16

22 Roundworms exhibit an important evolutionary adaptation, a digestive tube with two openings, a mouth and an anus –A complete digestive tract can process food and absorb nutrients efficiently

23 Phylum Mollusca –Is represented by soft-bodied animals, but most are protected by a hard shell –Includes snails, slugs, clams, octopuses, and squids, to name a few Invertebrates - Mollusks

24 The body of a mollusk has three main parts: a muscular foot, a visceral mass, and a mantle Figure Mantle Mantle cavity Shell Anus Gill Foot Nerve cords Visceral mass Kidney Coelom Heart Reproductive organs Digestive tract Radula Mouth

25 The three major classes of mollusks are 1. Gastropods, which are protected by a single, spiraled shell Figure 17.18a

26 2. Bivalves, protected by shells divided into two halves Figure 17.18b

27 3. Cephalopods, which may or may not have a shell Figure 17.18c

28 Phylum Annelida –Includes worms with body segmentation Invertebrates - Annelids Figure Mouth Brain Accessory hearts Main heart Coelom Nerve cord Digestive tract Blood vessels Segment walls Excretory organ Anus

29 There are three main classes of annelids 1. Earthworms, which eat their way through soil Figure 17.20a

30 2. Polychaetes, which burrow in the sea floor Figure 17.20b

31 3. Leeches, some of which are parasitic Figure 17.20c

32 Phylum Arthropoda –Contains organisms named for their jointed appendages –Includes crustaceans, arachnids, and insects Invertebrates - Arthropods

33 Arthropods are segmented animals with specialized segments and appendages General Characteristics of Arthropods Figure Antennae (sensory reception) Pincer (defense) Cephalothorax Head Thorax Mouthparts (feeding) Walking legs Abdomen Swimming appendages

34 The body of an arthropod is completely covered by an exoskeleton

35 There are four main groups of arthropods 1. Arachnids, such as spiders, scorpions, ticks, and mites Arthropod Diversity Figure 17.22

36 2. Crustaceans, such as crabs, lobsters, crayfish, shrimps, and barnacles Figure 17.23

37 3. Millipedes and centipedes Figure 17.24

38 Hawk moth Mosquito Paper wasp Damselfly Water strider Ground beetle Antenna Eye Head Mouthparts Thorax Forewing Abdomen Hindwing Grasshopper 4. Insects, most of which have a three-part body Figure 17.25

39 Many insects undergo metamorphosis in their development Figure (a) Larva (caterpillar) (b) Pupa (c) Pupa (d) Emerging adult (e) Adult

40 Phylum Echinodermata –Is named for the spiny surfaces of the organisms –Includes sea stars, sand dollars, sea urchins, and sea cucumbers Invertebrates - Echinoderms Figure 17.27

41 Echinoderms –Are all marine –Lack body segments –Usually have an endoskeleton –Have a water vascular system that facilitates gas exchange and waste disposal

42 Vertebrates –Are represented by mammals, birds, reptiles, amphibians, and fishes –Have unique features, including the cranium and backbone THE VERTEBRATE GENEALOGY Figure 17.28

43 Phylum Chordata –Includes the subphylum of vertebrates Characteristics of Chordates

44 Other subphyla include the lancelets and tunicates, which share four key chordate characteristics Figure 17.29

45 The four chordate hallmarks are –A dorsal, hollow nerve cord –A notochord –Pharyngeal slits –A post-anal tail

46 Figure Muscle segments Post-anal tail Notochord Anus Dorsal, hollow nerve cord Pharyngeal slits Brain Mouth

47 An overview of chordate and vertebrate evolution

48 Figure Eras Cenozoic Mesozoic Paleozoic Precambrian Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Tunicates Lancelets Agnatha (jawless vertebrates, such as lampreys) Chondrichthyes (sharks and rays) Osteichthyes (bony fishes) Amphibia (frogs and salamanders) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Ancestral chordate Vertebrae Jaws Lungs or lung derivatives Legs Amniotic egg Hair Feathers Chordates Vertebrates Tetrapods Amniotes Periods

49 The first vertebrates probably evolved during the early Cambrian period, about 540 million years ago These early vertebrates, the agnathans, lacked jaws –Agnathans are represented today by lampreys Fishes

50 The two major groups of living fishes are the classes –Chondrichthyes or cartilaginous fishes –Osteichthyes or bony fishes

51 Cartilaginous fishes have a flexible skeleton made of cartilage –Sharks have a lateral line system sensitive to vibrations in the water Figure 17.32a

52 Bony fishes –Have a skeleton reinforced by hard calcium salts –Have a lateral line system, a keen sense of smell, and excellent eyesight Figure 17.32b

53 Members of the class Amphibia –Exhibit a mixture of aquatic and terrestrial adaptations –Usually need water to reproduce Amphibians Figure 17.33

54 Amphibians –Were the first vertebrates to colonize land –Descended from fishes that had lungs and fins with muscles Figure Lobe-finned fish Early amphibian

55 Class Reptilia –Includes snakes, lizards, turtles, crocodiles, and alligators –Can live totally on land Reptiles

56 Adaptations for living on land include –Scales to prevent dehydration –Lungs for breathing –The amniotic egg Figure 17.35

57 Reptiles are ectotherms that obtain their body heat from the environment –Cold blooded Reptiles diversified extensively during the Mesozoic Era

58 Dinosaurs included the largest animals ever to live on land Figure 17.36

59 Class Aves –Evolved during the great reptilian radiation of the Mesozoic era –Evolved the ability to fly Birds

60 Bird anatomy and physiology are modified for flight –Bones are honeycombed, which makes them lighter –Some specific organs are absent, which reduces weight –A warm, constant body temperature is maintained through endothermy

61 A bird’s wings –Illustrate the same principles of aerodynamics as the wings of an airplane Figure Airfoil

62 Class Mammalia –Evolved from reptiles about 225 million years ago –Includes mostly terrestrial organisms Two features are mammalian hallmarks –Hair –Mammary glands that produce milk and nourish the young Mammals

63 There are three major groups of mammals –Monotremes, the egg-laying mammals, constitute the first group Figure 17.38a

64 –The second group of mammals, marsupials, are the so-called pouched mammals Most mammals are born rather than hatched and are nurtured inside the mother by an organ called a placenta Figure 17.38b

65 –Eutherians are also called placental mammals Their placentas provide more intimate and long- lasting association between the mother and her developing young than do marsupial placentas Figure 17.38c

66 Primate evolution –Provides a context for understanding human origins Primates –Evolved from insect-eating mammals during the late Cretaceous period Early primates –Were small, arboreal mammals The Evolution of Primates

67 The distinguishing characteristics of primates were shaped by the demands of living in trees –Limber shoulder joints –Eyes in front of the face –Excellent eye-hand coordination –Extensive parental care Figure 17.39

68 –Apes, the closest relatives to humans Figure 17.40d–g

69 Humans and apes have shared a common ancestry for all but the last 5–7 million years The Emergence of Humankind

70 Figure Prosimians Anthropoids Monkeys Apes Prosimians (lemurs, lorises, pottos, and tarsiers) New World monkeys Old World monkeys Gibbons Orangutans Gorillas Chim- panzees Humans Ancestral primate

71 Our ancestors were not chimpanzees or any other modern apes Chimpanzees and humans represent two divergent branches of the anthropoid tree Some Common Misconceptions

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