CHAPTER 18 The Evolution of Animal Diversity

BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor

From PowerPoint® Lectures for Biology: Concepts & Connections

CHAPTER 18The Evolution of Animal Diversity

Modules 18.1 – 18.4


• 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?

What Am I?


• 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?


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

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


• Animals are eukaryotic, multicellular heterotrophs that ingest their food

– They lack cell walls

– They also have unique intercellular junctions

18.1 What is an animal?ANIMAL EVOLUTION AND DIVERSITY

Figure 18.1A


• Most animals are diploid except for haploid eggs and sperm

• Animals proceed through a well-defined life cycle

Figure 18.1B

1

2

3

45

6

DIPLOID

MeiosisSperm

Eggs

Zygote(fertilized egg)

Blastula(cross section)

Early gastrula(cross section)

Later gastrula(cross section)

Outer cell layer(ectoderm)

Inner cell layer(endoderm)

Opening

Larva

Digestivetract

Met

amor

phos

is

Adult7

HAPLOID


• Cells in these protists gradually became more specialized and layered

18.2 The animal kingdom probably originated from colonial protists

Figure 18.2

1 Early colony of protists;aggregate ofidentical cells

2 Hollow sphere(shown incross section)

3 Beginningof cellspecialization(cross section)

4 Infolding(cross section)

5 Gastrula-like“protoanimal”(cross section)

Digestivecavity

Reproductivecells

Somaticcells


• 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


• Organisms in the phylum Porifera are among the simplest animals

– Many sponges are radially symmetrical

– Their parts are arranged around a central axis

18.3 Sponges have a relatively simple, porous bodyINVERTEBRATES

Figure 18.3A, B

Central axis


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

Figure 18.3C

Pores

WATERFLOW

Skeletalfiber

Centralcavity

Choanocyte

Amoebocyte

Choanocyte incontact withan amoebocyte

Flagella


• The sponge lineage arose very early– They probably

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

Figure 18.3D, E

Single cell

Stalk


• Cnidarians are the simplest animals with tissues

• These animals exist in two radially symmetrical forms– Polyps, such as hydra, corals, and sea

anemones

18.4 Cnidarians are radial animals with stinging threads

Figure 18.4A, C


– Medusas, the jellies

Figure 18.4B


• Cnidocytes on their tentacles sting prey

– 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


Figure 18.4D

TentacleCoiledthread

Capsule(nematocyst)

“Trigger”

CNIDOCYTE

Prey

Dischargeof thread


• These animals have mirror-image right and left sides

– They also have a head with sensory structures

– They move headfirst through their environment

18.5 Most animals are bilaterally symmetrical

Figure 18.5

Dorsal

Posterior

Ventral

Anterior


• 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

18.6 Flatworms are the simplest bilateral animals

Figure 18.6A

Digestive tract(gastrovascularcavity)

Nerve cords

Mouth

Eyespots

Nervoustissue clusters

Bilateral symmetry


• Flukes and tapeworms are parasitic flatworms with complex life cycles

Figure 18.6B

Mature flukes in bloodvessels of intestine

Humanhost

Male

Female

Snail host

1 Sexual reproductionof flukes in human;fertilized eggs passout in feces

2 Eggs hatchin water

3 Larvathatinfectssnail

4 Asexual reproductionof flukes in snail

5 Larva thatinfects human

6 Larva penetratesskin andblood vessels


• A tapeworm

Units withreproductive

structures

HeadHooksSucker

Figure 18.6C


• Sponges, cnidarians, and flatworms lack a body cavity

18.7 Most animals have a body cavity

Figure 18.7A

Body covering(from ectoderm)

Tissue-filled region(from mesoderm)

Digestive tract(from endoderm)


• Nearly all other animals have a body cavity

• 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


Figure 18.7B, C


Muscle layer(from mesoderm)Pseudocoelom



Tissue layerlining coelomand suspendinginternal organs(from mesoderm)

Coelom



• 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

18.8 Roundworms have a pseudocoelom and a complete digestive tract


• Many nematodes are free-living

Figure 18.8A, B

Trichinella juvenile Muscle tissue

– Others are parasites


• Phylum Mollusca is a large and diverse phylum that includes

– gastropods, such as snails and slugs

18.9 Diverse mollusks are variations on a common body plan

Figure 18.9B, C


– bivalves, such as clams and scallops

Figure 18.9D


– cephalopods, such as squids and octopuses

Figure 18.9E, F


• All mollusks have a muscular foot and a mantle– 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


Figure 18.9A

VISCERAL MASS

Coelom

Heart

Reproductiveorgans

Digestivetract

Shell

RADULA

Mouth

Nervecords

Kidney

MANTLE

Mantlecavity

Anus

Gill

FOOT

Radula

Mouth


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

18.10 Many animals have a segmented body

Figure 18.10A

Anus

Segmentwalls

Excretory organ

Digestivetract

Coelom

Mainheart

Brain

Mouth

Accessoryheart

Nerve cord

Blood vessels


• Segmentation probably evolved as an adaptation for movement

Figure 18.10B, C


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

– An earthworm eats its way through soil

18.11 Earthworms and other annelids are segmented worms


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

Figure 18.11A, B


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

Figure 18.11C


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

18.12 Arthropods are the most numerous and widespread of all animals


Figure 18.12A

Antennae(sensoryreception)

Cephalothorax Abdomen

Head

Thorax

Swimmingappendages

Walking legs

Mouthparts (feeding)Pincer (defense)


• In terms of numbers, distribution, and diversity, they are the most successful phylum of animals– Horseshoe crabs are ancient marine

arthropods

Figure 18.12B


• Most arachnids are terrestrial and carnivorous

Figure 18.12C


• Crustaceans are nearly all aquatic

Figure 18.12D


• Millipedes and centipedes make up a fourth group of arthropods

Figure 18.12E


• 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

18.13 Insects are the most diverse group of organisms


Figure 18.13A

Antenna Forewing

MouthpartsHindwing

Head Thorax Abdomen

Eye


• The insects you see here undergo incomplete metamorphosis

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

Figure 18.13B, C


• The insects you see here undergo complete metamorphosis

Figure 18.13D, E


– They have larvae specialized for eating and growing

– The larvae look very different from the adults

– Adults are specialized for dispersal and reproduction

Figure 18.13F, G

Haltere


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

– These organisms are radially symmetrical as adults

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

Figure 18.14B, C


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

Figure 18.14A

Stomach

Anus

Spines

TUBE FEET

CANALS


• 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

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


• The simplest chordates are tunicates and lancelets– These are marine invertebrates

Figure 18.15A

POST-ANAL TAIL

DORSAL, HOLLOWNERVE CORD

PHARYNGEALSLITS

MouthMuscle

segments

NOTOCHORD

LARVA


• Lancelets

Figure 18.15B

HeadNOTOCHORD

DORSAL, HOLLOWNERVE CORD

Mouth

PharynxPHARYNGEALSLITS Digestive

tract

Water exit

Segmentalmuscles

Anus POST-ANALTAIL


• Most chordates are vertebrates

– Their endoskeletons include a skull

– Their backbone is composed of vertebrae

18.16 A skull and a backbone are hallmarks of vertebrates

VERTEBRATES

Figure 18.16

Vertebrae Backbone Skull


• Lampreys lack hinged jaws

– They are classified as agnathans

18.17 Most vertebrates have hinged jaws

Figure 18.17A, B

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

Gillslits

Skeletalrods

Skull

Mouth


• There are two classes of fish

– Chondrichthyes, cartilaginous fishes such as sharks

– Osteichthyes, bony fishes such as tuna and trout

18.18 Fishes are jawed vertebrates with gills and paired fins

Figure 18.18A


• Bony fishes are more diverse and have– more mobile fins

– operculi that move water over the gills

– a buoyant swim bladder

Figure 18.18B

BONY SKELETON

SWIM BLADDERGills

OPERCULUM


• There are three major classes of bony fishes– Ray-finned

fishes

– Lobe-finned fishes

– Lungfishes

Figure 18.18C

Rainbow trout,a ray-fin

Coelacanth,a lobe-fin


• Class Amphibia is represented today by

– frogs

– toads

– salamanders

18.19 Amphibians were the first land vertebrates


• Amphibians were the first terrestrial vertebrates– Their limbs

allow them to move on land

– However, amphibian larvae must develop in water

Figure 18.19A-C


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

Figure 18.19D

Bonessupporting gills

Typical tetrapod limb skeleton


• 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

18.20 Reptiles have more terrestrial adaptations than amphibians

Figure 18.20A, B


• Dinosaurs were the most diverse reptiles to inhabit land– This group included some of the largest

land animals ever

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

Figure 18.20C


• Like reptiles, class Aves has

– scales

– amniotic eggs

18.21 Birds share many features with their reptilian ancestors

Figure 18.21A

Teeth(like reptile)

Wing claw(like reptile)

Feathers

Long tail withmany vertebrae(like reptile)


• Other bird characteristics include– wings

– feathers

– an endothermic metabolism

– hollow bones

– a highly efficient circulatory system

Figure 18.21B, C


• 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

18.22 Mammals also evolved from reptiles


• 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


• Marsupials have a short gestation

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

– Example: kangaroos

Figure 18.22B


• Most mammals are eutherians, also called placentals– They have a

relatively long gestation

– Complete embryonic development occurs within the mother

Figure 18.22C


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

18.23 A phylogenetic tree gives animal diversity an evolutionary perspective

PHYLOGENY OF THE ANIMAL KINGDOM


Figure 18.23A

Porifera Platyhelminthes Mollusca Arthropoda Chordata

EchinodermataAnnelidaNematodaCnidaria

No body cavityPseudocoelom PROTOSTOMES

Coelom fromcell masses

DEUTEROSTOMESCoelom from

digestive tube

True coelom

Body cavity

Bilateralsymmetry

True tissues

Ancestral protists

Radialsymmetry

No true tissues

Presentday


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

Figure 18.23B

Lophotrochozoa Ecdysozoa

Protostomes Deuterostomes

Bilateral symmetryRadial symmetry

No true tissues True tissues

Ancestral colonialchoanoflagellate

POR

IFER

A

CN

IDA

RIA

PLA

TYH

ELM

INTH

ES

MO

LLU

SCA

AN

NEL

IDA

NEM

ATO

DA

AR

THR

OPO

DA

ECH

INO

DER

MA

TA

CH

OR

DA

TA


• Introduced species are threatening Australia’s native animals

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

Figure 18.24A-D

CHAPTER 18 The Evolution of Animal Diversity

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