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The Development of the Animal Kingdom

Explore the evolution and diversity of animals in this informative chapter, covering topics such as animal reproduction, body symmetry, and the development of true tissues and body cavities. Learn about the major branches of animal phylogeny and the characteristics of invertebrates. Discover fascinating details about sponges, cnidarians, flatworms, roundworms, and mollusks.

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The Development of the Animal Kingdom

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  1. 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. Haploid Sperm Egg • 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 2 1 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 Opening Figure 17.3

  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 Infolding Gastrula-like “proto-animal” Early colony of protists (aggregate of identical cells) Hollow sphere (shown in cross section) Beginning of cell specialization 4 2 5 3 1 Figure 17.4

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

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

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

  9. Tissue-filled region (from mesoderm) Body covering (from ectoderm) • 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 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. 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 Visceral mass Reproductive organs Coelom Mantle Heart Kidney 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 Excretory organ Blood vessels 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. 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 Hindwing Mosquito Paper wasp Mouthparts 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 Figure 17.26 (e) Adult

  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. Chordates Vertebrates Tetrapods Amniotes Periods Eras Cenozoic Aves (birds) Tertiary Mammalia (mammals) Tunicates Lancelets Reptilia (reptiles) Cretaceous Amphibia (frogs and salamanders) Osteichthyes (bony fishes) Agnatha (jawless vertebrates, such as lampreys) Mesozoic 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. 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

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