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The Development of the Animal Kingdom

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1 The Development of the Animal Kingdom
CHAPTER 25 The Development of the Animal Kingdom Honors Biology

2 What Is an Animal? Animals
Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion Digest their food within their bodies 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 Haploid Sperm Egg 1 2 Meiosis Fertilization Zygote (fertilized egg) Adult 3 Diploid Blastula (cross section) 7 Metamorphosis Digestive tract Outer cell layer (ectoderm) 4 Primitive gut 6 5 Early gastrula Larva Inner cell layer (endoderm) Later gastrula Figure 17.3 Opening

4 Early Animals and the Cambrian Explosion
Animals probably evolved from a colonial protist that lived in the Precambrian seas Digestive cavity Reproductive cells Somatic cells 1 Early colony of protists (aggregate of identical cells) 2 Hollow sphere (shown in cross section) 3 Beginning of cell specialization 4 Infolding 5 Gastrula-like “proto-animal” Figure 17.4

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

6 Four key evolutionary branch points have been hypothesized
Animal Phylogeny 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

7 4 3 2 1 Coelom from digestive tube Pseudocoelom True coelom
Sponges Cnidarians Flatworms Roundworms Mollusks Annelids Arthropods Echinoderms Chordates Coelom from cell masses Coelom from digestive tube 4 Pseudocoelom True coelom No body cavity 3 Body cavities Radial symmetry Bilateral symmetry 2 True tissues 1 Multicellularity Figure 17.6

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

9 May be a pseudocoelom or a true coelom
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 Body covering (from ectoderm) Tissue-filled region (from mesoderm) Digestive tract (from endoderm) (a) No body cavity (e.g., flatworm) Pseudocoelom Body covering (from ectoderm) Digestive tract (from endoderm) Muscle layer (from mesoderm) (b) Pseudocoelom (e.g., roundworm) Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Mesentery (c) True coelom (e.g., annelid) Figure 17.8

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

12 Invertebrates - Sponges
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 Figure 17.9

13 Choanocyte in contact with an amoebocyte
Pores Water flow Skeleton fiber Central cavity Choanocyte Flagella Amoebocyte Figure 17.10

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 Polyp form Medusa 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 Coiled thread Tentacle Capsule “Trigger” Cnidocyte Discharge of thread Prey Figure 17.13

19 Invertebrates - Flatworms
Phylum Platyhelminthes Is represented by the simplest bilateral animals Includes free-living forms such as planarians Digestive tract (gastrovascular cavity) Nerve cords Mouth Eyespots Nervous tissue clusters Figure 17.14

20 Some flatworms are parasitic
Blood flukes are an example Tapeworms parasitize many vertebrates, including humans Head Reproductive structures Hooks Sucker Figure 17.15

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

24 The body of a mollusk has three main parts: a muscular foot, a visceral mass, and a mantle
Reproductive organs Coelom Mantle Kidney Heart Digestive tract Mantle cavity Radula Shell Radula Anus Gill Mouth Nerve cords Foot Mouth Figure 17.17

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 Invertebrates - Annelids
Phylum Annelida Includes worms with body segmentation Anus Brain Main heart Coelom Digestive tract Segment walls Mouth Accessory hearts Nerve cord Blood vessels Excretory organ Figure 17.19

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

33 General Characteristics of Arthropods
Arthropods are segmented animals with specialized segments and appendages Cephalothorax Abdomen Thorax Antennae (sensory reception) Head Swimming appendages Walking legs Pincer (defense) Mouthparts (feeding) Figure 17.21

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

35 There are four main groups of arthropods
Arthropod Diversity There are four main groups of arthropods 1. Arachnids, such as spiders, scorpions, ticks, and mites 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 4. Insects, most of which have a three-part body
Head Thorax Abdomen Hawk moth Antenna Forewing Eye Mosquito Paper wasp Mouthparts Hindwing Grasshopper Damselfly Water strider Ground beetle Figure 17.25

39 Many insects undergo metamorphosis in their development
(a) Larva (caterpillar) (b) Pupa (c) Pupa (d) Emerging adult (e) Adult Figure 17.26

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

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

43 Characteristics of Chordates
Phylum Chordata Includes the subphylum of vertebrates

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 Dorsal, hollow nerve cord
Notochord Brain Muscle segments Mouth Anus Pharyngeal slits Post-anal tail Figure 17.30

47 An overview of chordate and vertebrate evolution

48 Lungs or lung derivatives
Chordates Vertebrates Tetrapods Periods Amniotes Eras Cenozoic Tunicates Tertiary Aves (birds) Lancelets Mammalia (mammals) Reptilia (reptiles) Cretaceous Amphibia (frogs and salamanders) Mesozoic Agnatha (jawless vertebrates, such as lampreys) Osteichthyes (bony fishes) Feathers Jurassic Chondrichthyes (sharks and rays) Triassic Permian Hair Carboniferous Amniotic egg Devonian Paleozoic Legs Silurian Lungs or lung derivatives Ordovician Jaws Cambrian Vertebrae Precambrian Ancestral chordate Figure 17.31

49 These early vertebrates, the agnathans, lacked jaws
Fishes 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

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

54 Amphibians Were the first vertebrates to colonize land
Descended from fishes that had lungs and fins with muscles Lobe-finned fish Early amphibian Figure 17.34

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

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

57 Reptiles diversified extensively during the Mesozoic Era
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 Birds Class Aves Evolved during the great reptilian radiation of the Mesozoic era Evolved the ability to fly

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 Airfoil Figure 17.37

62 Two features are mammalian hallmarks
Mammals 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

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 The Evolution of Primates
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

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

70 Prosimians Anthropoids Monkeys Apes Chim-panzees Humans Gibbons
Gorillas Humans Orangutans New World monkeys Old World monkeys Prosimians (lemurs, lorises, pottos, and tarsiers) Ancestral primate Figure 17.41

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

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