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

42. THE VERTEBRATE GENEALOGY
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