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					CHAPTER 25
             The
             Development
             of the Animal
             Kingdom

Honors Biology
What Is an Animal?
• Animals
  – Are eukaryotic, multicellular, heterotrophic
    organisms that obtain nutrients by ingestion
  – Digest their food within their bodies




                                                   Figure 17.2
• Most animals                                                Haploid
                                                                          Sperm
                                                        Egg
  reproduce
                                                1                                2
  sexually and then
                                      Meiosis                                   Fertilization
  proceed through a
                                                                             Zygote
  series of                                         Adult
                                                                        (fertilized egg)


  developmental                                               Diploid
                                                                                                3
                                                                                Blastula
  stages                            7 Metamorphosis
                                                                                 (cross
                                                                                section)

                                            Digestive tract        Outer cell
• Most animals                                                       layer
                                                        Primitive (ectoderm)
                                                                                           4

                                                           gut
  have muscle cells                                 6
                                                                          5

  and nerve cells                  Larva                                                       Early
                                                                                               gastrula
  that control the              Inner cell layer                        Later gastrula
                                  (endoderm)
  muscles         Figure 17.3                             Opening
Early Animals and the Cambrian Explosion


• Animals probably evolved from a colonial protist
  that lived in the Precambrian seas

                                                                           Digestive
                                                                           cavity




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




                                                                                       Figure 17.4
• At the beginning of the Cambrian period, 545 million
  years ago, animals underwent a rapid diversification




                                               Figure 17.5
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
Sponges   Cnidarians   Flatworms Roundworms Mollusks              Annelids   Arthropods Echinoderms   Chordates




                                                                 Coelom from        Coelom from
                                                                 cell masses
                                                                                    digestive tube
                                                                             4
                                                Pseudocoelom
                                                                    True coelom

                                     No body
                                     cavity
                                                      3 Body cavities
                       Radial
                       symmetry           Bilateral
                                    2 symmetry

                           True tissues
                       1

               Multicellularity

                                                                                                          Figure 17.6
– The second major evolutionary split is based partly
  on body symmetry




 (a) Radial symmetry                (b) Bilateral symmetry




                                                         Figure 17.7
– Third, the evolution of                                Body covering Tissue-filled
                                                         (from         region
                                                         ectoderm)     (from
  body cavities led to                                                 mesoderm)


  more complex animals                                                     Digestive
  A body cavity                                                            tract (from
                                                                           endoderm)
                                     (a) No body cavity (e.g., flatworm)
                                                       Pseudocoelom
   • Is a fluid-filled                                                     Body
                                                                           covering
                                                                           (from
     space separating the                                                  ectoderm)


     digestive tract from                          Digestive
                                                   tract (from             Muscle
                                                   endoderm)               layer (from
     the outer body wall             (b) Pseudocoelom (e.g., roundworm)
                                                                           mesoderm)

                                                          Coelom       Body covering
   • May be a                                                          (from ectoderm)
                                                                         Tissue layer
     pseudocoelom or a                                                   lining
                                                                         coelom and
                                                   Digestive             suspending
     true coelom                                   tract (from Mesentery internal
                                                   endoderm)             organs
                                                                         (from
                                     (c) True coelom (e.g., annelid)     mesoderm)
                       Figure 17.8
– Fourth, among animals with a true coelom, there are
  two main evolutionary branches, which differ in
  embryonic development
THE KINGDOM ANIMALIA

• Divided into invertebrates and vertebrates
  – Invertebrates are animals without backbones
     • Represent 95% of the animal kingdom
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
                 Choanocyte
                 in contact
Pores            with an
                 amoebocyte
Water flow

Skeleton fiber



Central cavity


Choanocyte       Flagella
Amoebocyte




                              Figure 17.10
Invertebrates - Cnidarians


• Phylum Cnidaria
  – Is characterized by organisms with radial symmetry
    and tentacles with stinging cells
• 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
• Examples of polyps are
  – Hydras, sea anemones,
    and coral animals




                            Figure 17.12
• The organisms we call jellies are medusas
• Cnidarians are carnivores that use tentacles armed
  with cnidocytes, or “stinging cells,” to capture prey


                                                   Coiled
                       Tentacle                    thread    Capsule




                                  “Trigger”
                                                            Cnidocyte
                                    Discharge of
                                    thread




              Prey
                                                                        Figure 17.13
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
• Some flatworms
  are parasitic
  – Blood flukes are                           Head


    an example
  – Tapeworms
                       Reproductive
    parasitize many    structures

    vertebrates,
    including
    humans                            Hooks


                                      Sucker



                                               Figure 17.15
Invertebrates - Roundworms
• Phylum Nematoda
  – Includes the most diverse
    and widespread of all
    animals
  – Occurs in aquatic and moist
    terrestrial habitats




                           Figure 17.16
• 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
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
• The body of a mollusk has three main parts: a
  muscular foot, a visceral mass, and a mantle

                           Visceral mass


                                    Reproductive
                    Coelom          organs
   Mantle      Kidney       Heart
                                           Digestive
                                           tract
     Mantle
     cavity
                                                                 Radula
     Shell                                             Radula
     Anus

     Gill                                                Mouth


                        Nerve cords
        Foot                                                        Mouth


                                                                    Figure 17.17
• The three major classes of mollusks are
  1. Gastropods, which are protected by a single, spiraled
    shell




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




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




                                               Figure 17.18c
Invertebrates - Annelids
• Phylum Annelida
  – Includes worms with body segmentation


                                                              Anus

                    Brain
                             Main
                             heart
                                Coelom
                                    Digestive
                                    tract
                                            Segment
        Mouth                               walls



            Accessory
            hearts
                        Nerve cord
                                     Blood        Excretory
                                     vessels      organ              Figure 17.19
• There are three main classes of annelids
  1. Earthworms, which eat their way through soil




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




                                                Figure 17.20b
3. Leeches, some of which are parasitic




                                          Figure 17.20c
Invertebrates - Arthropods
• Phylum Arthropoda
  – Contains organisms named for their jointed
    appendages
  – Includes crustaceans, arachnids, and insects
General Characteristics of Arthropods
• Arthropods are segmented animals with specialized
  segments and appendages
                   Cephalothorax             Abdomen



                     Thorax
       Antennae
        (sensory   Head
      reception)


                                                            Swimming
                                                            appendages




                                                  Walking
                                                  legs
      Pincer
      (defense)           Mouthparts (feeding)
                                                                         Figure 17.21
• The body of an arthropod is completely covered by
  an exoskeleton
Arthropod Diversity
• There are four main groups of arthropods
   1. Arachnids, such as spiders, scorpions, ticks, and
     mites




                                                          Figure 17.22
2. Crustaceans, such as crabs, lobsters, crayfish,
  shrimps, and barnacles




Figure 17.23
3. Millipedes and centipedes




                               Figure 17.24
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
• Many insects
  undergo
  metamorphosis in
  their development
                                 (a) Larva
                                 (caterpillar)

                                                      (b) Pupa

                                                                 (c) Pupa




                  (d) Emerging
                         adult


                                          (e) Adult                   Figure 17.26
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
• Echinoderms
  – Are all marine
  – Lack body segments
  – Usually have an endoskeleton
  – Have a water vascular system that facilitates gas
    exchange and waste disposal
THE VERTEBRATE GENEALOGY
• Vertebrates
  – Are represented by
    mammals, birds,
    reptiles,
    amphibians, and
    fishes
  – Have unique
    features, including
    the cranium and
    backbone

                           Figure 17.28
Characteristics of Chordates
• Phylum Chordata
  – Includes the subphylum of vertebrates
• Other subphyla include the lancelets and tunicates,
  which share four key chordate characteristics




                                                  Figure 17.29
• The four chordate hallmarks are
  – A dorsal, hollow nerve cord
  – A notochord
  – Pharyngeal slits
  – A post-anal tail
                                  Dorsal,
                                  hollow
                                  nerve cord
                   Notochord

                                               Brain


 Muscle segments




                                                Mouth

                      Anus

                               Pharyngeal
Post-anal                      slits
tail

                                               Figure 17.30
• An overview of chordate and vertebrate evolution
         Precambrian                                                                          Paleozoic                                                  Mesozoic                    Cenozoic   Eras
                                                Cambrian   Ordovician Silurian Devonian Carboniferous                            Permian   Triassic    Jurassic         Cretaceous   Tertiary   Periods

                                                                                                                                                                             Tunicates


                                                                                                                                                                             Lancelets




               Ancestral chordate
                                                                                                                                 Agnatha (jawless vertebrates,
                                                                                                                                            such as lampreys)




                                    Vertebrae
                                                    Jaws
                                                                                                                         Chondrichthyes (sharks and rays)


                                                                                                                                     Osteichthyes (bony fishes)
                                                                                                                                                                                                                                         Chordates




                                                                                                                                                      Amphibia (frogs and
                                                                                                Legs




                                                                                                                                                           salamanders)
                                                                  Lungs or lung derivatives
                                                                                                                                                                                                                           Vertebrates




                                                                                                                                                           Reptilia (reptiles)
                                                                                                          Amniotic egg
                                                                                                                          Hair




                                                                                                                                                                                 Aves
                                                                                                                                                                               (birds)
                                                                                                                                                             Feathers
                                                                                                                                                                                                               Tetrapods




                                                                                                                                                                           Mammalia
                                                                                                                                                                                                    Amniotes




                                                                                                                                                                          (mammals)
Figure 17.31
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
• The two major groups of living fishes are the classes
   – Chondrichthyes or cartilaginous fishes
   – Osteichthyes or bony fishes
• Cartilaginous fishes have a flexible skeleton made
  of cartilage
  – Sharks have a lateral line system sensitive to
    vibrations in the water




                                                     Figure 17.32a
• 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
Amphibians
• Members of the class
  Amphibia
  – Exhibit a mixture of
    aquatic and terrestrial
    adaptations
  – Usually need water to
    reproduce




                              Figure 17.33
• 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
Reptiles
• Class Reptilia
   – Includes snakes, lizards, turtles, crocodiles, and
     alligators
   – Can live totally on land
• Adaptations for living
  on land include
  – Scales to prevent
    dehydration
  – Lungs for breathing
  – The amniotic egg




                           Figure 17.35
• Reptiles are ectotherms that obtain their body heat
  from the environment
   – Cold blooded

• Reptiles diversified extensively during the Mesozoic
  Era
• Dinosaurs included the largest animals ever to live
  on land




                                                  Figure 17.36
Birds
• Class Aves
  – Evolved during the great reptilian radiation of the
    Mesozoic era
  – Evolved the ability to fly
• 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
• A bird’s wings
  – Illustrate the same principles of aerodynamics as the
    wings of an airplane




                                                     Figure 17.37
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
• There are three major groups of mammals
  – Monotremes, the egg-laying mammals, constitute the
    first group




                                                 Figure 17.38a
– 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
– 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
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
• 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
– Apes, the closest
  relatives to humans




                        Figure 17.40d–g
 The Emergence of Humankind

• Humans and apes have
  shared a common
  ancestry for all but the
  last 5–7 million years
                          Prosimians (lemurs, lorises, pottos, and tarsiers)
                                                                                         Prosimians




                                                      New World monkeys




      Ancestral primate
                                                       Old World monkeys
                                                                               Monkeys




                                                                   Gibbons



                                                               Orangutans
                                                                                         Anthropoids

                                                                               Apes




                                                                   Gorillas


                                                                     Chim-
                                                                   panzees


                                                                   Humans
Figure 17.41
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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