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0. Chapter 18. The Evolution of Animal Diversity. 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 classifying an animal isn’t always easy.

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Chapter 18

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Chapter 18

The Evolution of Animal Diversity


  • 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 classifying an animal isn’t always easy


  • Imagine you were the first person to encounter the animal pictured here

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


A Tasmanian tiger, 1928

  • Biologists often encounter classification problems

    • When evolution creates organisms with similar characteristics


Figure 18.1A

What is an animal?

  • Animals are eukaryotic, multicellular heterotrophs

    • That ingest their food

ANIMAL EVOLUTION AND DIVERSITY


  • Animal development

    • May include a blastula, gastrula, and larval stage

Key

Haploid (n)

Diploid (2n)

Sperm

2

1

Egg

Meiosis

Zygote(fertilized egg)

3

Eight-cell stage

Adult

8

Metamorphosis

4

Blastula(cross section)

Digestive tract

Ectoderm

5

Larva

7

Early gastrula(cross section)

6

Endoderm

Futuremesoderm

Figure 18.1B

Internal sac

Later gastrula(cross section)


The ancestor of animals was probably a colonial, flagellated protist

  • Cells in these protists

    • Gradually became more specialized and layered

Somaticcells

Digestive

cavity

Reproductivecells

2Hollow sphere of unspecialized cells (shown in cross section)

3Beginning of cell specialization (cross section)

4Infolding (cross section)

1Colonial protist, an aggregate of identical cells

5Gastrula-like “proto-animal” (cross section)

Figure 18.2A


Figure 18.2B

  • Animal diversity exploded during the Cambrian period


Top

Dorsal surface

Anterior

end

Posterior end

Ventral surface

Bottom

Figure 18.3A

Animals can be characterized by basic features of their “body plan”

  • Animal body plans may vary in symmetry


Tissue-filled region

(from mesoderm)

Body covering

(from ectoderm)

Digestive tract

(from endoderm)

Body covering

(from ectoderm)

Muscle layer

(from mesoderm)

Digestive tract

(from endoderm)

Pseudocoelom

Body covering

(from ectoderm)

Coelom

Tissue layer

lining coelomand suspendinginternal organs(from mesoderm)

Digestive tract(from endoderm)

  • Vary in body cavity

Figure 18.3B–D


  • Development as either protostomes or deuterostomes

  • Together these animals show bilateral symmetry and three germ layers

  • Distinction between each is found in embryonic development


Molluscs

Annelids

Sponges

Flatworms

Chordates

Arthropods

Cnidarians

Nematodes

Echinoderms

Deuterostomes

Protostomes

Bilaterians

Radial symmetry

Bilateral symmetry

Eumetazoans

No true tissues

True tissues

Figure 18.4

Ancestral

colonial protist

The body plans of animals can be used to build phylogenetic trees

  • One hypothesis of animal phylogeny is based on morphological comparisons


Invertebrates


Figure 18.5A–C

Sponges have a relatively simple, porous body

  • Sponges, phylum Porifera

    • Are the simplest animals and have no true tissues

INVERTEBRATES


Pores

Choanocyte

Amoebocyte

Waterflow

Skeletalfiber

Centralcavity

Flagella

Choanocytein contactwith anamoebocyte

Figure 18.5D

  • Flagellated choanocytes

    • Filter food from the water passing through the porous body


Cnidarians are radial animals with tentacles and stinging cells

  • Cnidarians, phylum Cnidaria

    • Have true tissues and radial symmetry


Figure 18.6A–C

  • Their two body forms are

    • Polyps, such as hydra

    • Medusae, the jellies


Capsule(nematocyst)

Coiledthread

Tentacle

“Trigger”

Dischargeof thread

Prey

Cnidocyte

Figure 18.6D

  • They have a gastrovascular cavity

    • And cnidocytes on tentacles that sting prey


Flatworms are the simplest bilateral animals

  • Flatworms, phylum Platyhelminthes

    • Are bilateral animals with no body cavity


Gastrovascularcavity

Nerve cords

Mouth

Eyespots

Nervoustissueclusters

Figure 18.7A

Bilateral symmetry

  • A planarian has a gastrovascular cavity

    • And a simple nervous system

Planaria


Units withreproductivestructures

Scolex(anteriorend)

HooksSucker

Colorized SEM 80

  • Flukes and tapeworms

    • Are parasitic flatworms with complex life cycles

Figure 18.7B


Nematodes have a pseudocoelom and a complete digestive tract

  • Nematodes, phylum Nematoda

    • Have a pseudocoelom and a complete digestive tract

    • Are covered by a protective cuticle


Muscle tissue

Trichinella juvenile

Mouth

Colorized SEM 400

LM 350

Figure18.8A, B

  • Many nematodes are free-living

    • And others are plant or animal parasites


Visceral mass

Reproductive

organs

Coelom

Heart

Kidney

Digestive

tract

Mantle

Shell

Digestive tract

Mantle

cavity

Radula

Radula

Anus

Mouth

Gill

Mouth

Foot

Nerve

cords

Figure 18.9A

Diverse molluscs are variations on a common body plan

  • All molluscs have a muscular foot and a mantle

    • Which may secrete a shell that encloses the visceral mass

  • Many mollusks

  • Feed with a rasping radula


Figure 18.9B, C

  • Gastropods

    • Gastropods are the largest group of molluscs

      • And include the snails and slugs


Figure 18.9D

  • Bivalves

    • The bivalves have shells divided into two halves

      • And include clams, oysters, mussels, and scallops


Figure 18.9E, F

  • Cephalopods

    • Cephalopods are adapted to be agile predators

      • And include squids, cuttlefish and octopuses


Annelids are segmented worms

  • The segmented bodies of phylum Annelida

    • Give them added mobility for swimming and burrowing


Epidermis

Anus

Circular

muscle

Segment wall

(partition

between

segments)

Segment

wall

Longitudinal

muscle

Dorsal

vessel

Excretory

organ

Mucus-secreting

organ

Intestine

Bristles

Bristles

Dorsal

vessel

Coelom

Nerve cord

Ventral vessel

Excretory

organ

Digestive

tract

Brain

Segment

wall

Blood vessels

Giant

Australian

earthworm

Mouth

Nerve cord

Pumping segmental vessels

  • Earthworms and Their Relatives

    • Earthworms

      • Eat their way through soil

      • Have a closed circulatory system

Figure 18.10A


Figure 18.10B, C

  • Polychaetes

    • Form the largest group of annelids

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


Figurer 18.10D

  • Leeches

    • Most leeches

      • Are free-living carnivores, but some suck blood


Cephalothorax

Abdomen

Thorax

Antennae

(sensory

reception)

Head

Swimming

appendages

Walking legs

Figure 18.11A

Mouthparts (feeding)

Pincer (defense)

Arthropods are segmented animals with jointed appendages and an exoskeleton

  • The diversity and success of arthropods is largely related to their segmentation, exoskeleton, and jointed appendages


Colorized SEM 900

A black widow spider (about

1 cm wide)

A dust mite (about 420

µm long)

A scorpion (about 8 cm long)

Figure 18.11B, C

  • Chelicerates

    • Chelicerates include

      • Horseshoe crabs

      • Arachnids, such as spiders, scorpions, mites, and ticks


Figure 18.11D

  • Millipedes and Centipedes

    • Millipedes and centipedes

      • Are identified by the number of jointed legs per body segment


Figure 18.11E

  • Crustaceans

    • The crustaceans

      • Are nearly all aquatic

      • Include crabs, shrimps, and barnacles


Insects are the most diverse group of organisms

  • Insects have a three-part body consisting of

    • Head, thorax, and abdomen

    • Three sets of legs

    • Wings (most, but not all insects)


  • Many insects undergo

    • Incomplete or complete metamorphosis


Abdomen

Head

Thorax

Antenna

Forewing

Eye

Mouthparts

Hindwing

  • A. Order Orthoptera

    • The order orthoptera includes

      • Grasshoppers, crickets, katydids, and locusts

Figure 18.12A


Figure 18.12B

  • B. Order Odonata

    • The order odonata includes

      • Dragonflies and damselflies


Figure 18.12C

  • C. Order Hemiptera

    • The order hemiptera includes

      • Bedbugs, plant bugs, stinkbugs, and water striders


Figure 18.12D

  • D. Order Coleoptera

    • The order coleoptera includes

      • Beetles


Figure 18.12E

  • E. Order Lepidoptera

    • The order lepidoptera includes

      • Moths and butter flies


Haltere

Figure 18.12F

  • F. Order Diptera

    • The order Diptera includes

      • Flies, fruit flies, houseflies, gnats, and mosquitoes


Figure 18.12G

  • G. Order Hymenoptera

    • The order hymenoptera includes

      • Ants, bees, and wasps


Tube foot

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

  • Echinoderms, phylum Echinodermata

    • Includes organisms such as sea stars and sea urchins

    • Are radially symmetrical as adults

Tube foot

Spine

Figure 18.13B, C


Anus

Spines

Stomach

Tube feet

Canals

Figure 18.13A

  • The water vascular system

    • Has suction cup–like tube feet used for respiration and locomotion


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


Excurrent

siphon

Post-anal tail

Dorsal, hollow

nerve cord

Head

Pharyngeal

slits

Notochord

Mouth

Mouth

Muscle

segments

Pharynx

Dorsal,

hollow

nerve cord

Pharyngeal

slits

Notochord

Digestive tract

Water exit

Post-anal

tail

Adult

(about 3 cm high)

Larva

Segmental

muscles

Anus

Figure 18.14A, B

  • The simplest chordates are tunicates and lancelets

    • Marine invertebrates that use their pharyngeal slits for suspension feeding


Chordates

Craniates

Vertebrates

Jawed vertebrates

Tetrapods

Amniotes

Lobe-fins

Reptiles

Lancelets

Mammals

Hagfishes

Tunicates

Lampreys

Amphibians

Milk

Sharks, rays

Ray-finned fishes

Amniotic egg

Legs

Lobed fins

Lungs or lung derivatives

Jaws

Vertebral column

Head

Brain

Ancestral chordate

Derived characters define the major clades of chordates

  • A chordate phylogenetic tree

    • Is based on a sequence of derived characters

VERTEBRATES

Figure 18.15


  • Most chordates are vertebrates

    • With a head and a backbone made of vertebrae


Figure 18.16A

Lampreys are vertebrates that lack hinged jaws

  • Lampreys lack hinged jaws and paired fins


Skeletal

rods

Skull

Gill

slits

Mouth

Figure 18.16B

  • Most vertebrates have hinged jaws

    • Which may have evolved from skeletal supports of the gill slits


Jawed vertebrates with gills and paired fins include sharks, ray-finned fishes, and lobe-fins

  • Three lineages of jawed vertebrates with gills and paired fins

    • Are commonly called fishes


Figure 18.17A

  • Chondrichthyans

    • Chondrichthyans

      • Have a flexible skeleton made of cartilage

      • Include sharks and rays


Bony skeleton

Dorsal fin

Gills

Anal fin

Operculum

Swim bladder

Pectoral fin

Pelvic fin

Heart

Rainbow trout,

a ray-fin

Figure 18.17B

  • Ray-finned Fishes (e.g. Atlantic herring, Ocean sunfish)

    • The ray-finned fishes have

      • A skeleton reinforced with a hard matrix of calcium phosphate

      • Operculi that move water over the gills

      • A buoyant swim bladder


Figure 18.17C

  • Lobe-fins (e.g. coelacanths, lungfish)

    • The lobe-fin fishes

      • Have muscular fins supported by bones


Bones

supporting

gills

Tetrapod

limb

skeleton

Figure 18.18A

Amphibians were the first tetrapods—vertebrates with two pairs of limbs

  • Amphibians

    • Were the first tetrapods with limbs allowing movement on land


Figure 18.18B–D

  • Include frogs, toads, salamanders, and caecilians

  • Most amphibian embryos and larvae still must develop in water


Figure 18.19A, B

Reptiles are amniotes—tetrapods with a terrestrially adapted egg

  • Terrestrial adaptations of reptiles include

    • Waterproof scales

    • A shelled, amniotic egg


  • Living reptiles other than birds are ectothermic


Figure 18.19C

  • Dinosaurs, the most diverse reptiles to inhabit land

    • Included some of the largest animals ever to inhabit land

    • May have been endothermic, producing their own body heat


Wing claw

(like dinosaur)

Teeth

(like dinosaur)

Long tail with

many vertebrae

(like dinosaur)

Feathers

Figure 18.20A

Birds are feathered reptiles with adaptations for flight

  • Birds evolved from

    • A lineage of small, two-legged dinosaurs called theropods


Figure 18.20B

  • Birds are reptiles that have

    • Wings, feathers, endothermic metabolism, and many other adaptations related to flight


Figure 18.20C

  • Flight ability is typical of birds

    • But there are a few flightless species


Mammals are amniotes that have hair and produce milk

  • Mammals are endothermic amniotes with

    • Hair, which insulates their bodies

    • Mammary glands, which produce milk


Mammals


Figure 18.21A

  • Monotremes lay eggs


  • Monotremes lay eggs


Figure 18.21B

  • The embryos of marsupials and eutherians are nurtured by the placenta within the uterus

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


Figure 18.21C

  • Eutherians, placental mammals

    • Complete development before birth


An animal phylogenetic tree is a work in progress

  • Molecular-based phylogenetic trees

    • Distinguish two protostome clades: the lophotrochozoans and the ecdysozoans

Molluscs

Annelids

Sponges

Chordates

Arthropods

Flatworms

Nematodes

Cnidarians

Echinoderms

Deuterostomes

Ecdysozoans

Lophotrochozoans

ANIMAL PHYLOGENY AND DIVERSITY REVISITED

Bilaterians

Radial symmetry

Bilateral symmetry

Eumetazoans

No true tissues

True tissues

Figure 18.22

Ancestral

colonial protist


Figure 18.23A-D

Humans threaten animal diversity by introducing non-native species

  • Introduced species

    • Are threatening Australia’s native animals

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