Chapter 18 the evolution of animal diversity
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CHAPTER 18 The Evolution of Animal Diversity. Modules 18.1 – 18.4. What Am I?. Of some 1.5 million species of organisms known to science, over two-thirds are animals Humans have a long history of studying animal diversity But do we always know what an animal is when we see one?.

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CHAPTER 18 The Evolution of Animal Diversity

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Chapter 18 the evolution of animal diversity

CHAPTER 18The Evolution of Animal Diversity

Modules 18.1 – 18.4


What am i

What Am I?

  • Of some 1.5 million species of organisms known to science, over two-thirds are animals

  • Humans have a long history of studying animal diversity

    • But do we always know what an animal is when we see one?


Chapter 18 the evolution of animal diversity

  • Imagine you were the first person to encounter this duck-billed platypus

  • It has webbed feet, a bill, a furry body, mammary glands, and it lays eggs

    • With all of its varying characteristics, what would you think it is?


Chapter 18 the evolution of animal diversity

  • Biologists often encounter classification problems when evolution creates organisms with similar characteristics

  • Marsupials, such as this Tasmanian tiger, are a good example


18 1 what is an animal

ANIMAL EVOLUTION AND DIVERSITY

18.1 What is an animal?

  • Animals are eukaryotic, multicellular heterotrophs that ingest their food

    • They lack cell walls

    • They also have unique intercellular junctions

Figure 18.1A


Chapter 18 the evolution of animal diversity

HAPLOID

Meiosis

Sperm

Eggs

1

Metamorphosis

2

  • Most animals are diploid except for haploid eggs and sperm

7

Adult

  • Animals proceed through a well-defined life cycle

Digestivetract

Zygote(fertilized egg)

3

DIPLOID

Larva

6

Outer cell layer(ectoderm)

Inner cell layer(endoderm)

Blastula(cross section)

Opening

4

5

Later gastrula(cross section)

Early gastrula(cross section)

Figure 18.1B


18 2 the animal kingdom probably originated from colonial protists

18.2 The animal kingdom probably originated from colonial protists

  • Cells in these protists gradually became more specialized and layered

Digestivecavity

Reproductivecells

Somaticcells

3

1

2

Early colony of protists;aggregate ofidentical cells

Hollow sphere(shown incross section)

Beginningof cellspecialization(cross section)

4

5

Infolding(cross section)

Gastrula-like“protoanimal”(cross section)

Figure 18.2


Chapter 18 the evolution of animal diversity

  • Ecological, geologic, or genetic factors may have caused the Cambrian explosion in animal diversity

  • Cambrian fossils can be classified as ancient representatives of the familiar animal phyla


18 3 sponges have a relatively simple porous body

INVERTEBRATES

18.3 Sponges have a relatively simple, porous body

  • Organisms in the phylum Porifera are among the simplest animals

    • Many sponges are radially symmetrical

    • Their parts are arranged around a central axis

Central axis

Figure 18.3A, B


Chapter 18 the evolution of animal diversity

Choanocyte incontact withan amoebocyte

  • Flagellated choanocytes filter food from the water passing through the porous body

Pores

WATERFLOW

Skeletalfiber

Centralcavity

Choanocyte

Flagella

Amoebocyte

Figure 18.3C


Chapter 18 the evolution of animal diversity

  • They probably evolved from multicellular choanoflagellates, the group that most likely gave rise to the animal kingdom

  • The sponge lineage arose very early

Single cell

Stalk

Figure 18.3D, E


18 4 cnidarians are radial animals with stinging threads

18.4 Cnidarians are radial animals with stinging threads

  • Cnidarians are the simplest animals with tissues

  • These animals exist in two radially symmetrical forms

    • Polyps, such as hydra, corals, and sea anemones

Figure 18.4A, C


Chapter 18 the evolution of animal diversity

  • Medusas, the jellies

Figure 18.4B


Chapter 18 the evolution of animal diversity

  • The tentacles, controlled by nerves, then push the food through the mouth into a gastrovascular cavity

  • In the cavity, the food is digested and then distributed

  • In cnidarians, only two cell layers are produced during gastrulation

  • Cnidocytes on their tentacles sting prey


Chapter 18 the evolution of animal diversity

Capsule(nematocyst)

Coiledthread

Tentacle

“Trigger”

Dischargeof thread

Prey

CNIDOCYTE

Figure 18.4D


18 5 most animals are bilaterally symmetrical

18.5 Most animals are bilaterally symmetrical

  • These animals have mirror-image right and left sides

    • They also have a head with sensory structures

    • They move headfirst through their environment

Dorsal

Posterior

Anterior

Ventral

Figure 18.5


18 6 flatworms are the simplest bilateral animals

18.6 Flatworms are the simplest bilateral animals

  • Phylum Platyhelminthes

    • Planarians have a simple nervous system consisting of a brain, sense organs, and branching nerves

    • As in cnidarians, the mouth of a flatworm is the only opening for its gastrovascular cavity

Digestive tract(gastrovascularcavity)

Nerve cords

Mouth

Eyespots

Nervoustissue clusters

Figure 18.6A

Bilateral symmetry


Chapter 18 the evolution of animal diversity

Mature flukes in bloodvessels of intestine

Male

Humanhost

Female

  • Flukes and tapeworms are parasitic flatworms with complex life cycles

1

Sexual reproductionof flukes in human;fertilized eggs passout in feces

6

Larva penetratesskin andblood vessels

2

Eggs hatchin water

5

Larva thatinfects human

3

Larvathatinfectssnail

4

Asexual reproductionof flukes in snail

Snail host

Figure 18.6B


Chapter 18 the evolution of animal diversity

  • A tapeworm

Units withreproductivestructures

Head

Hooks

Sucker

Figure 18.6C


18 7 most animals have a body cavity

18.7 Most animals have a body cavity

  • Sponges, cnidarians, and flatworms lack a body cavity

Tissue-filled region(from mesoderm)

Body covering(from ectoderm)

Digestive tract(from endoderm)

Figure 18.7A


Chapter 18 the evolution of animal diversity

  • This cavity is a fluid-filled space between the digestive tract and the body wall

    • The cavity aids in movement, cushions organs, and it may help in circulation

  • Nearly all other animals have a body cavity


Chapter 18 the evolution of animal diversity

Body covering(from ectoderm)

Muscle layer(from mesoderm)

Pseudocoelom

Digestive tract(from endoderm)

Body covering(from ectoderm)

Coelom

Tissue layerlining coelomand suspendinginternal organs(from mesoderm)

Digestive tract(from endoderm)

Figure 18.7B, C


18 8 roundworms have a pseudocoelom and a complete digestive tract

18.8 Roundworms have a pseudocoelom and a complete digestive tract

  • Nematodes have a body cavity not completely lined by mesoderm

  • Like most animals, they possess a complete digestive tract

    • This is a tube with a mouth and an anus


Chapter 18 the evolution of animal diversity

Trichinella juvenile

Muscle tissue

  • Many nematodes are free-living

  • Others are parasites

Figure 18.8A, B


18 9 diverse mollusks are variations on a common body plan

18.9 Diverse mollusks are variations on a common body plan

  • Phylum Mollusca is a large and diverse phylum that includes

    • gastropods, such as snails and slugs

Figure 18.9B, C


Chapter 18 the evolution of animal diversity

  • bivalves, such as clams and scallops

Figure 18.9D


Chapter 18 the evolution of animal diversity

  • cephalopods, such as squids and octopuses

Figure 18.9E, F


Chapter 18 the evolution of animal diversity

  • The mantle may secrete a shell which encloses the visceral mass

  • Mollusks have a true coelom and a circulatory system

    • Many mollusks feed with a rasping radula

    • All mollusks have a muscular foot and a mantle


    Chapter 18 the evolution of animal diversity

    VISCERAL MASS

    Coelom

    Reproductiveorgans

    Kidney

    Heart

    Digestivetract

    MANTLE

    Shell

    Mantlecavity

    Radula

    RADULA

    Anus

    Gill

    Mouth

    FOOT

    Nervecords

    Mouth

    Figure 18.9A


    18 10 many animals have a segmented body

    18.10 Many animals have a segmented body

    • Segmentation is the subdivision of some or most of the body into a series of repeated parts, or segments

    Anus

    Brain

    Mainheart

    Coelom

    Digestivetract

    Segmentwalls

    Mouth

    Accessoryheart

    Nerve cord

    Figure 18.10A

    Excretory organ

    Blood vessels


    Chapter 18 the evolution of animal diversity

    • Segmentation probably evolved as an adaptation for movement

    Figure 18.10B, C


    18 11 earthworms and other annelids are segmented worms

    18.11 Earthworms and other annelids are segmented worms

    • The segmented bodies of annelids (phylum Annelida) give them added mobility for swimming and burrowing

      • An earthworm eats its way through soil


    Chapter 18 the evolution of animal diversity

    • Polychaetes search for prey on the seafloor or live in tubes and filter food particles

    Figure 18.11A, B


    Chapter 18 the evolution of animal diversity

    • Most leeches are free-living carnivores, but some suck blood

    Figure 18.11C


    18 12 arthropods are the most numerous and widespread of all animals

    18.12 Arthropods are the most numerous and widespread of all animals

    • Arthropods (phylum Arthropoda) are segmented animals with exoskeletons and jointed appendages


    Chapter 18 the evolution of animal diversity

    Cephalothorax

    Abdomen

    Thorax

    Head

    Antennae(sensoryreception)

    Swimmingappendages

    Walking legs

    Pincer (defense)

    Mouthparts (feeding)

    Figure 18.12A


    Chapter 18 the evolution of animal diversity

    • Horseshoe crabs are ancient marine arthropods

    • In terms of numbers, distribution, and diversity, they are the most successful phylum of animals

    Figure 18.12B


    Chapter 18 the evolution of animal diversity

    • Most arachnids are terrestrial and carnivorous

    Figure 18.12C


    Chapter 18 the evolution of animal diversity

    • Crustaceans are nearly all aquatic

    Figure 18.12D


    Chapter 18 the evolution of animal diversity

    • Millipedes and centipedes make up a fourth group of arthropods

    Figure 18.12E


    18 13 insects are the most diverse group of organisms

    18.13 Insects are the most diverse group of organisms

    • Insects are the most numerous and successful arthropods

    • They have a three-part body consisting of

      • head, thorax, and abdomen

      • three sets of legs

      • wings (most, but not all insects)

    • The development of many insects includes metamorphosis


    Chapter 18 the evolution of animal diversity

    Thorax

    Abdomen

    Head

    Antenna

    Forewing

    Eye

    Hindwing

    Mouthparts

    Figure 18.13A


    Chapter 18 the evolution of animal diversity

    • Their young resemble adults, but are smaller with different body proportions

    • The insects you see here undergo incomplete metamorphosis

    Figure 18.13B, C


    Chapter 18 the evolution of animal diversity

    • The insects you see here undergo complete metamorphosis

    Figure 18.13D, E


    Chapter 18 the evolution of animal diversity

    • The larvae look very different from the adults

    • Adults are specialized for dispersal and reproduction

    • They have larvae specialized for eating and growing

    Haltere

    Figure 18.13F, G


    18 14 echinoderms have spiny skin an endoskeleton and a water vascular system for movement

    18.14 Echinoderms have spiny skin, an endoskeleton, and a water vascular system for movement

    • Phylum Echinodermata includes organisms such as sea stars and sea urchins

      • These organisms are radially symmetrical as adults

    Figure 18.14B, C


    Chapter 18 the evolution of animal diversity

    • The water vascular system has suction-cup-like tube feet used for respiration and locomotion

    Anus

    Spines

    Stomach

    TUBE FEET

    CANALS

    Figure 18.14A


    18 15 our own phylum chordata is distinguished by four features

    18.15 Our own phylum, Chordata, is distinguished by four features

    • Organisms in this phylum are segmented animals with four distinctive features

      • Dorsal hollow nerve cord

      • Stiff notochord

      • Pharyngeal slits behind the mouth

      • Muscular post-anal tail


    Chapter 18 the evolution of animal diversity

    • These are marine invertebrates

    • The simplest chordates are tunicates and lancelets

    POST-ANAL TAIL

    DORSAL, HOLLOWNERVE CORD

    PHARYNGEALSLITS

    Musclesegments

    Mouth

    NOTOCHORD

    LARVA

    Figure 18.15A


    Chapter 18 the evolution of animal diversity

    • Lancelets

    DORSAL, HOLLOWNERVE CORD

    NOTOCHORD

    Head

    Mouth

    Water exit

    Anus

    Pharynx

    POST-ANALTAIL

    PHARYNGEALSLITS

    Digestivetract

    Segmentalmuscles

    Figure 18.15B


    18 16 a skull and a backbone are hallmarks of vertebrates

    VERTEBRATES

    18.16 A skull and a backbone are hallmarks of vertebrates

    • Most chordates are vertebrates

      • Their endoskeletons include a skull

      • Their backbone is composed of vertebrae

    Vertebrae

    Backbone

    Skull

    Figure 18.16


    18 17 most vertebrates have hinged jaws

    18.17 Most vertebrates have hinged jaws

    • Lampreys lack hinged jaws

      • They are classified as agnathans

    • Jaws evolved by the modification of skeletal supports of the gill slits

    Gillslits

    Skeletalrods

    Skull

    Mouth

    Figure 18.17A, B


    18 18 fishes are jawed vertebrates with gills and paired fins

    18.18 Fishes are jawed vertebrates with gills and paired fins

    • There are two classes of fish

      • Chondrichthyes, cartilaginous fishes such as sharks

      • Osteichthyes, bony fishes such as tuna and trout

    Figure 18.18A


    Chapter 18 the evolution of animal diversity

    • more mobile fins

    • operculi that move water over the gills

    • a buoyant swim bladder

    • Bony fishes are more diverse and have

    BONY SKELETON

    OPERCULUM

    Gills

    SWIM BLADDER

    Figure 18.18B


    Chapter 18 the evolution of animal diversity

    • Ray-finned fishes

    • Lobe-finned fishes

    • Lungfishes

    Rainbow trout,a ray-fin

    • There are three major classes of bony fishes

    Coelacanth,a lobe-fin

    Figure 18.18C


    18 19 amphibians were the first land vertebrates

    18.19 Amphibians were the first land vertebrates

    • Class Amphibia is represented today by

      • frogs

      • toads

      • salamanders


    Chapter 18 the evolution of animal diversity

    • Their limbs allow them to move on land

    • However, amphibian larvae must develop in water

    • Amphibians were the first terrestrial vertebrates

    Figure 18.19A-C


    Chapter 18 the evolution of animal diversity

    • Air-breathing lungfishes that developed skeleton-reinforced appendages probably gave rise to the first amphibians

    Bonessupporting gills

    Typical tetrapod limb skeleton

    Figure 18.19D


    18 20 reptiles have more terrestrial adaptations than amphibians

    18.20 Reptiles have more terrestrial adaptations than amphibians

    • Class Reptilia is able to live on land due to

      • waterproof scales

      • a shelled, amniotic egg

    • Modern reptiles are ectotherms

      • They warm their bodies by absorbing heat from the environment

    Figure 18.20A, B


    Chapter 18 the evolution of animal diversity

    • This group included some of the largest land animals ever

    • They may have been endothermic, producing their own body heat

    • Dinosaurs were the most diverse reptiles to inhabit land

    Figure 18.20C


    18 21 birds share many features with their reptilian ancestors

    18.21 Birds share many features with their reptilian ancestors

    Wing claw(like reptile)

    Teeth(like reptile)

    • Like reptiles, class Aves has

      • scales

      • amniotic eggs

    Feathers

    Long tail withmany vertebrae(like reptile)

    Figure 18.21A


    Chapter 18 the evolution of animal diversity

    • wings

    • feathers

    • an endothermic metabolism

    • hollow bones

    • a highly efficient circulatory system

    • Other bird characteristics include

    Figure 18.21B, C


    18 22 mammals also evolved from reptiles

    18.22 Mammals also evolved from reptiles

    • Class Mammalia descended from reptiles

    • Mammals are endothermic

    • There are two unique mammalian characteristics

      • Hair, which insulates the body

      • Mammary glands, which produce milk that nourishes their young


    Chapter 18 the evolution of animal diversity

    • Most mammals give birth to young after a period of embryonic development inside the body of the mother

    • The embryo is nurtured by an organ called the placenta

  • A few mammalslay eggs

    • Monotremes

  • Figure 18.22A


    Chapter 18 the evolution of animal diversity

    • The tiny offspring complete development attached to the mother’s nipple, usually inside a pouch

    • Example: kangaroos

    • Marsupials have a short gestation

    Figure 18.22B


    Chapter 18 the evolution of animal diversity

    • They have a relatively long gestation

    • Complete embryonic development occurs within the mother

    • Most mammals are eutherians, also called placentals

    Figure 18.22C


    18 23 a phylogenetic tree gives animal diversity an evolutionary perspective

    PHYLOGENY OF THE ANIMAL KINGDOM

    18.23 A phylogenetic tree gives animal diversity an evolutionary perspective

    • A traditional phylogenetic tree is based on patterns of embryonic development and some fundamental structures


    Chapter 18 the evolution of animal diversity

    Presentday

    Porifera

    Platyhelminthes

    Mollusca

    Arthropoda

    Chordata

    Cnidaria

    Nematoda

    Annelida

    Echinodermata

    Pseudocoelom

    PROTOSTOMESCoelom fromcell masses

    DEUTEROSTOMESCoelom fromdigestive tube

    No body cavity

    True coelom

    Body cavity

    Radialsymmetry

    Bilateralsymmetry

    No true tissues

    True tissues

    Figure 18.23A

    Ancestral protists


    Chapter 18 the evolution of animal diversity

    ECHINODERMATA

    PLATYHELMINTHES

    ARTHROPODA

    NEMATODA

    CHORDATA

    MOLLUSCA

    PORIFERA

    ANNELIDA

    CNIDARIA

    • A molecular-based tree has added two clades within the protostomes

    Lophotrochozoa

    Ecdysozoa

    Protostomes

    Deuterostomes

    Radial symmetry

    Bilateral symmetry

    True tissues

    No true tissues

    Ancestral colonialchoanoflagellate

    Figure 18.23B


    18 24 connection humans threaten animal diversity by introducing non native species

    18.24 Connection: Humans threaten animal diversity by introducing non-native species

    • Introduced species are threatening Australia’s native animals

    Figure 18.24A-D


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