18.1 What is an animal? - Staff Web Sites @ BBHCSDstaff.bbhcsd.org/gardnere/files/2013/02/Chapter-18-Student-Notes.pdf · Chapter 18 The Evolution of ... – presence of true tissues,

© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey

Chapter 18Chapter 18 The Evolution ofInvertebrate Diversity

Most octopuses rely on nonaggressive defensemechanisms such as camouflage.

The blue-ringed octopus is an exception, with

– a toxin 10,000 times more lethal than cyanide and

– sapphire-blue circles that proclaim its identity.

Introduction

© 2012 Pearson Education, Inc.

Figure 18.0_1Chapter 18: Big Ideas

Animal Evolutionand Diversity

Invertebrate Diversity

Animal Phylogeny andDiversity Revisited

Figure 18.0_2

ANIMAL EVOLUTIONAND DIVERSITY


Animals are

– eukaryotic,

– multicellular heterotrophs, and

– have cells that lack cell walls.

Animals also use ingestion, the eating of food.

Fungi absorb nutrients after digesting food outsidetheir body.

18.1 What is an animal?


Figure 18.1A

Most adult animals are diploid and reproducesexually.

– The eggs and sperm

– are produced by meiosis,

– are the only haploid cells, and

– fuse during fertilization to form a zygote.

– The zygote divides by mitosis to form a hollow ball ofcells called a blastula.



Video: Sea Urchin Embryonic Development

One side of the blastula folds in and cells becomerearranged to form a gastrula that establishesthree embryonic layers.

– Endoderm forms a lining of the future digestive tract.

– Ectoderm forms an outer layer that will give rise to theskin and nervous system.

– Mesoderm forms a middle layer that will give rise tomuscles and most internal organs.



After the gastrula stage, many animals developdirectly into adults.

Other animals, such as the sea star, develop intoone or more larval stages.

– A larva is an immature individual that looks different fromthe adult animal.

– A larva undergoes a major change in body form, calledmetamorphosis, and becomes a reproductively matureadult.

Clusters of master control homeotic genes controltransformation of the zygote into an adult animal.



Figure 18.1B_s8

KeyHaploid (n)

Diploid (2n)

MeiosisEgg

Adult

Metamorphosis

Digestive tract

Eight-cell stage

Blastula(cross section)

Zygote(fertilized egg)

EctodermLarva

Future mesoderm

Early gastrula(cross section)

Later gastrula(cross section)

Endoderm

Internal sac

Sperm

1

2

3

4

8

5

6

7

The oldest generally accepted animal fossils thathave been found are 575–550 million years old.

Animal diversification appears to have acceleratedrapidly from 535 to 525 million years ago, during theCambrian period, known as the Cambrian explosion.

The most celebrated source of Cambrian fossils isthe Burgess Shale containing a cornucopia ofperfectly preserved animal fossils.

18.2 Animal diversification began more than halfa billion years ago


Figure 18.2A

Spriggina floundersi (about 3 cm long)

Dickinsonia costata(about 8 cm across)

Figure 18.2B

Chordate

Arthropod

Anomalocaris

Hallucigenia

The Cambrian explosion may have been caused by

– increasingly complex predator-prey relationships or

– an increase in atmospheric oxygen.

Much of the diversity in body form among theanimal phyla is associated with variations in whereand when homeotic genes are expressed withindeveloping embryos.

Of the 35 or so animal phyla, all but one areinvertebrates, named because they lack vertebra.

18.2 Animal diversification began more than halfa billion years ago


Animal body plans vary in

– symmetry,

– presence of true tissues,

– number of embryonic layers,

– presence of a body cavity, and

– details of their embryonic development.

18.3 Animals can be characterized by basicfeatures of their “body plan”


Symmetry

– Animals that have radial symmetry have a top andbottom but lack back and front or right and left sides. Animaginary slice through the central axis divides them intomirror images.

– Animals with bilateral symmetry have mirror-imageright and left sides and a

– distinct head, or anterior end,

– tail, or posterior end,

– back, or dorsal, surface, and

– bottom, or ventral, surface.



Figure 18.3A

Dorsal surface

Ventral surfaceBottom

Anteriorend

Posteriorend

Top

Tissues

– Tissues are collections of specialized cells that performspecial functions.

– Sponges are the only animals that lack true tissues.

Embryonic layers

– Some animals have only ectoderm and endoderm.

– Most animals have

– ectoderm,

– mesoderm, and

– endoderm.



Animals with three embryonic layers may have abody cavity, a fluid-filled space between thedigestive tract and outer body wall that

– cushions internal organs and that

– enables them to grow and move independently of thebody wall.

– In soft-bodied animals, fluid in the body cavity forms ahydrostatic skeleton.

– A true coelom is completely lined by tissues derived frommesoderm.

– A pseudocoelom is a body cavity that is not completelylined by tissues derived from mesoderm.



Animals with three tissue layers can be separatedinto two groups based on details of their embryonicdevelopment. For example, the opening formedduring gastrulation develops into the

– mouth in protostomes and

– anus in deuterostomes.



Figure 18.3B

Coelom

Body covering(from ectoderm)

Tissue layerlining coelomand suspendinginternal organs(from mesoderm)

Digestive tract(from endoderm)

Figure 18.3C


Muscle layer(from mesoderm)

Digestive tract(from endoderm)

Pseudocoelom

Figure 18.3D


Tissue-filled region(from mesoderm)

Digestive sac(from endoderm)

Because animals diversified so rapidly on the scaleof geologic time, it is difficult to sort out theevolutionary relationships among phyla using thefossil record.

18.4 The body plans of animals can be used tobuild phylogenetic trees


One diagram of evolutionary relationships usesmorphology to construct a phylogenetic tree. Thistree distinguishes between

– sponges and eumetazoans (animals with true tissues),

– animals with radial or bilateral symmetry (bilaterians),and

– protostomes and deuterostomes.

All phylogenetic trees are hypotheses for the keyevents in the evolutionary history of animals.

Researchers are increasingly adding molecularcomparisons to the construction of these trees.

18.4 The body plans of animals can be used tobuild phylogenetic trees


Figure 18.4

No truetissues

Radialsymmetry

Ancestralcolonialprotist

Bilateralsymmetry

Truetissues

Pro

tos

tom

es

Eu

me

tazo

an

s Bila

teria

ns

De

ute

ros

tom

es

Sponges

Cnidarians

Flatworms

Nematodes

Annelids

Arthropods

Molluscs

Echinoderms

Chordates

INVERTEBRATE DIVERSITY


Sponges (phylum Porifera) are simple, sedentaryanimals without true tissues.

Water enters through pores in the body wall into acentral cavity and then flows out through a largeropening.

18.5 Sponges have a relatively simple, porous body


The body of a sponge consists of two layers ofcells separated by a gelatinous region.

– The inner layer of flagellated choanocytes filters foodand engulfs it by phagocytosis.

– Amoebocytes wander through the middle body regionand produce skeletal fibers composed of

– flexible protein and

– mineralized particles called spicules.



Figure 18.5A

A purple tubesponge

Scypha

An azure vase sponge

Figure 18.5B

Waterflow

Pores

Water flow

Flagellum

Amoebocyte

Pore

Choanocyte

Water flow

Choanocytein contact withan amoebocyte

Skeletal fiber

Centralcavity

Sponges are suspension feeders, filtering foodparticles from water passed through food-trappingequipment.

– To grow by 100 g, a sponge must filter roughly 1,000 kg ofwater.

– Choanocytes trap food particles in mucus on themembranous collars that surround their flagella.



Adult sponges are sessile and cannot escape frompredators. They deter pathogens, parasites, andpredators by producing

– defensive toxins and

– antibiotics.



Cnidarians (phylum Cnidaria)

– are characterized by radial symmetry and

– have only two tissue layers:

– an outer epidermis,

– an inner cell layer lining the digestive cavity, and

– a jelly-filled middle region may have scattered amoeboid cells.

18.6 Cnidarians are radial animals with tentaclesand stinging cells


Cnidarians exhibit two kinds of radially symmetricalbody forms.

– The most sedentary polyp body is cylindrical withtentacles projecting from one end.

– The more mobile medusa form is exemplified by amarine jelly.



Video: Coral Reef

Video: Jelly Swimming

Video: Hydra Budding

Figure 18.6A

A hydra(about 2–25mm tall)

A sea anemone(about 6 cm in diameter)

Figure 18.6B

A marine jelly(about 6 cm in diameter)

Cnidarians are carnivores that use their tentacles tocapture prey and to push prey into their mouths.

– The mouth leads to the gastrovascular cavity, whichfunctions in digestion and circulation and as a hydrostaticskeleton.

– Cnidocytes are unique stinging cells that capture preyand function in defense.



Video: Hydra Eating Daphnia (time lapse)

Video: Hydra Releasing Sperm

Video: Thimble Jellies

Video: Clownfish and Anemone

Figure 18.6C

Tentacle

Dischargeof thread“Trigger”

Coiled thread

Capsule

Prey

Cnidocyte

The vast majority of animal species belong to theclade Bilateria, consisting of animals with bilateralsymmetry.

Flatworms (phylum Platyhelminthes) are thesimplest bilaterians.

Flatworms live in marine, freshwater, and dampterrestrial habitats.

Some are parasitic and others are free-living.

18.7 Flatworms are the simplest bilateral animals


Figure 18.7A

Gastrovascularcavity

Nerve cords

Bilateral symmetryNervoustissue clusters

Mouth

Eyecups

There are three major groups of flatworms.

1. Free-living flatworms (planarians) have

– heads with light-sensitive eyespots,

– flaps to detect chemicals,

– dense clusters of nerve cells that form a simple brain and a pairof nerve cords that runs the length of the body, and

– a branched gastrovascular cavity with a single opening.



2. Flukes are parasitic flatworms with

– complex life cycles and

– suckers to attach to their hosts.

3. Tapeworms

– are parasitic,

– inhabit the digestive tracts of vertebrates,

– consist of a ribbonlike body with repeated units,

– have an anterior scolex armed with hooks and suckers thatgrasp the host,

– have no mouth, and simply absorb nutrients across their bodysurface.

– The units at the posterior end of tapeworms are full of ripe eggsthat pass out of the host’s body.



Figure 18.7B

Units withreproductivestructures

Scolex(anteriorend)

Hooks

Sucker

Nematodes or roundworms (phylum Nematoda)are abundant and diverse, with an estimated500,000 species. Nematodes have

– bilateral symmetry,

– three tissue layers,

– a nonliving cuticle covering the body that prevents themfrom drying out,

– a pseudocoelom body cavity that functions to distributenutrients and as a hydroskeleton, and

– a complete digestive tract with a mouth and anus.

18.8 Nematodes have a pseudocoelom and acomplete digestive tract


Although about 25,000 species of nematodes havebeen named, estimates of the total number ofspecies range as high as 500,000.

Humans host at least 50 species of parasiticnematodes.

18.8 Nematodes have a pseudocoelom and acomplete digestive tract


Video: C. elegans Crawling

Video: C. elegans Embryo Development (time lapse)

Figure 18.8A

Mouth

Figure 18.8B

Molluscs (phylum Mollusca) have

– a muscular foot that functions in locomotion,

– a visceral mass containing most of the internal organs,

– a mantle, which may secrete a shell that encloses thevisceral mass, and

– a true coelom and a circulatory system that pumps bloodthroughout the body.

– Many molluscs feed with a rasping radula, used to scrapeup food.

– The life cycle of many marine molluscs includes a ciliatedlarva called a trochophore.

18.9 Diverse molluscs are variations on a commonbody plan


Figure 18.9A

Visceral mass

Mantle

Kidney

Coelom

Heart

Mantlecavity

Anus

Reproductiveorgans

Digestivetract

Shell

Radula

Digestivetract Mouth

Nervecords

Foot

Gill

Figure 18.9B

Mouth

Anus

Gastropods are the largest group of molluscs andinclude the snails and slugs. Gastropods are

– found in fresh water, salt water, and terrestrialenvironments,

– the only molluscs that live on land, using the mantlecavity as a lung, and

– often protected by a single, spiral shell.

– Slugs have lost their mantle and shell and have longcolorful projections that function as gills.



Video: Nudibranchs

Bivalves

– include clams, oysters, mussels, and scallops and

– have shells divided into two halves that are hingedtogether.

– Most bivalves are sedentary suspension feeders,attached to the substrate by strong threads.



Figure 18.9C

A sea slug (about 5 cm long)A land snail

Figure 18.9D

Mussels (each about 6 cm long)

Eyes

A scallop(about 10 cmin diameter)

Cephalopods

– include squids, octopuses, and nautiluses,

– are fast, agile predators,

– have large brains and sophisticated sense organs,including complex image-focusing eyes, and

– a shell that is large in a nautilus, small and internal in asquid, or missing in an octopus.

– Squid are fast, streamlined predators that use amuscular siphon for jet propulsion.

– Octopuses live on the seafloor, where they creep aboutas active predators.



Figure 18.9E

A squid (internal shell)

A chambered nautilus (about 21 cm in diameter)

Annelids (phylum Annelida) have

– segmentation, the subdivision of the body along its lengthinto a series of repeated parts,

– a true coelom that functions as a hydrostatic skeleton,

– a nervous system that includes a simple brain and ventralnerve cord, and

– a closed circulatory system in which blood remainsenclosed in vessels throughout the body.

– Many invertebrates, such as molluscs and arthropods,have an open circulatory system in which blood ispumped through vessels into open body cavities.

18.10 Annelids are segmented worms


Annelids are found in damp soil, the sea, and mostfreshwater habitats.

The three groups of annelids are

– earthworms and their relatives,

– polychaetes, and

– leeches.

Earthworms ingest soil and extract nutrients,aerating soil and improving its texture.



Video: Tubeworms

Video: Earthworm Locomotion

Figure 18.10A

Anus

Bristles

Segmentwall

A giant Australianearthworm

Mucus-secretingorgan

Dorsalblood vessel

Digestivetract

Coelom

Brain

Excretoryorgan

Segmentwall

Ventral blood vessel

Pumping segmental vesselsNerve cordMouth

IntestineNerve cord

Ventralblood vessel

Bristles

Excretoryorgan

Dorsalbloodvessel

Longitudinalmuscle

Circularmuscle

EpidermisSegment wall(partitionbetweensegments)

Figure 18.10A_3

A giant Australian earthworm

Polychaetes are the largest group of annelids.

– Each polychaete segment has a pair of fleshyappendages with stiff bristles or chaetae.

– Polychaetes search for prey on the seafloor or live intubes and filter food particles.

Most leeches are free-living carnivores, but somesuck blood.

– Blood-sucking leeches use razor-like jaws, secrete ananesthetic and an anticoagulant, and suck up to 10times their own weight in blood.



Figure 18.10B

Tube-buildingpolychaetes

A sandworm A free-swimmingpolychaete

Figure 18.10C

There are over a million species of arthropods(phylum Arthropoda), including crayfish, lobsters,crabs, barnacles, spiders, ticks, and insects.

The diversity and success of arthropods are due totheir

– segmentation,

– a hard exoskeleton, and

– jointed appendages, for which the phylum is named.

18.11 Arthropods are segmented animals withjointed appendages and an exoskeleton


Arthropods have

– an open circulatory system and

– an exoskeleton, an external skeleton that protects theanimal but must be shed in the process of molting topermit growth.

– The body of most arthropods includes a head, thorax,and abdomen, although these segments may be fused.



Video: Lobster Mouth Parts

Figure 18.11A

Cephalothorax Abdomen

ThoraxHead

Antennae(sensoryreception)

Walking legs

Pincer (defense)Mouthparts (feeding)

Swimmingappendages

Figure 18.11B

Living arthropods represent four major lineages.

1. Chelicerates include horseshoe crabs and arachnids,such as spiders, scorpions, mites, and ticks.

– Most are terrestrial.

– Scorpions are nocturnal hunters.

– Spiders are a diverse group that typically hunt insects or trapthem in webs of silk that they spin from specialized glands ontheir abdomen.



Figure 18.11C

A scorpionA black widow spider(about 1 cm wide)

A dust mite(about 0.4 mm long)

Figure 18.11C_1

A scorpion

Figure 18.11C_2

A black widow spider(about 1 cm wide)

Figure 18.11C_3

A dust mite(about 0.4 mm long)

2. Millipedes and centipedes are identified by the numberof jointed legs per body segment.

– Millipedes are herbivores that have two pairs of short legs perbody segment.

– Centipedes are carnivores that have one pair of legs per bodysegment.



Figure 18.11D

Figure 18.11E

3. Crustaceans are nearly all aquatic. They include crabs,shrimp, and barnacles, which feed with jointedappendages.

4. Insects are the fourth lineage of arthropods, addressednext.



Figure 18.11F

A ghost crab(body about2.5 cm across)

Goose barnacles(about 2 cm high)

70% of all identified animal species are insects.

– There may be as many as 30 million insect species.

The body of an insect typically includes

– a head,

– thorax,

– abdomen,

– three sets of legs, and

– wings (with few exceptions).

18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals


The extraordinary success of insects is due to

– body segmentation,

– an exoskeleton,

– jointed appendages,

– flight,

– a waterproof cuticle, and

– a complex life cycle with short generations and largenumbers of offspring.



Insect life cycles often include metamorphosis,during which the animal takes on different bodyforms as it develops from larva to adult.

– More than 80% of insect species undergo completemetamorphosis in which a free-living larva transformsfrom a pupa into an adult.

– Other insect species undergo incompletemetamorphosis in which the transition from larva toadult is achieved through multiple molts, but withoutforming a pupa.



Video: Butterfly Emerging

Video: Bee Pollinating

Figure 18.12A

Larva (grub, upto 12 cm length)

Pupa

Adult (up to 4cm length)

Figure 18.12B

Antenna

Head Thorax Abdomen

Specializedjumping legs

Eye

MouthpartsWalking legs

Wings(extensions of cuticle)

Modular body plan

– The adult body parts of insects are formed by the fusionof embryonic segments identical to each other.

– The insect body plan is essentially modular in that eachembryonic segment develops independently.

– Homeotic genes act to modify the structure of insectsegments and their appendages.



Insect mouthparts are adapted for various types offeeding, such as

– chewing (grasshoppers),

– biting and tearing prey (mantids),

– lapping up fluids (houseflies), and

– piercing and sucking fluids of plants (aphids) andanimals (mosquitoes).



Insects have three pairs of legs, which are adaptedfor

– walking,

– jumping,

– grasping prey,

– digging in soil, or

– paddling on water.



Wings

– Most adult insects have one or two pairs of wings,allowing dispersal and escape from predators.

– Because wings are extensions of the cuticle, insectshave acquired flight without sacrificing any legs.

Protective color patterns

– Many insects have protective color patterns anddisguises, including modifications to antennae, wings,and bodies.



Figure 18.12C

A stick insectA leaf-mimic katydid

A caterpillar resemblinga bird dropping

Figure 18.12D

Figure 18.12E

Echinoderms (phylum Echinodermata) are

– a diverse group including sea stars, sand dollars, andsea urchins,

– slow-moving or sessile,

– all marine,

– radially symmetrical, and

– deuterostomes (along with the chordates).

18.13 Echinoderms have spiny skin, anendoskeleton, and a water vascular systemfor movement


Echinoderms have

– an endoskeleton of hard calcareous plates under a thinskin,

– a water vascular system based on a network of water-filled canals that branch into extensions called tube feet,and

– the ability to regenerate lost arms.

18.13 Echinoderms have spiny skin, anendoskeleton, and a water vascular systemfor movement


Video: Echinoderm Tube Feet

Figure 18.13A

Anus

Stomach

Spines

Tube feet

Canals

Figure 18.13B

Tube foot

Figure 18.13C

Spines

Tube feet

Chordates (phylum Chordata) are defined by

– a dorsal, hollow nerve cord,

– a flexible, supportive notochord,

– pharyngeal slits, and

– a muscular post-anal tail.

18.14 Our own phylum, Chordata, is distinguishedby four features


The simplest chordates are tunicates andlancelets, which

– do not have a backbone and

– use their pharyngeal slits for suspension feeding.

– Adult tunicates are stationary and attached, while thetunicate larva is a tadpole-like organism.

– Lancelets are small, bladelike chordates that live inmarine sands.

18.14 Our own phylum, Chordata, is distinguishedby four features


Figure 18.14A

Post-anal tail

Dorsal, hollownerve cord

Notochord

Mouth

Musclesegments

Pharyngealslits

LarvaAdult(about 3 cm high)

Excurrentsiphon

Figure 18.14B

Head

Mouth

Pharynx

Pharyngeal slits

Dorsal, hollownerve cord

Notochord

Post-anal tailWater exit

Anus

Segmental muscles

Digestive tract

ANIMAL PHYLOGENYAND DIVERSITY REVISITED


Biologists used evidence from the fossil record,morphology, and embryology to make hypothesesabout the evolutionary history of animal groups.

Recently, scientists have accumulated moleculardata such as DNA sequences that shed new lighton these phylogenetic relationships.

Figure 18.15 presents a slightly revised tree basedon this new molecular data.

18.15 An animal phylogenetic tree is a work inprogress


Figure 18.15No truetissues

Ancestralcolonialprotist

Radialsymmetry

Truetissues

Bilateralsymmetry

Sponges

Cnidarians

Flatworms

Molluscs

Annelids

Nematodes

Arthropods

Echinoderms

Chordates

Deu

tero

sto

mes

Ecd

yso

zo

an

sL

op

ho

troc

ho

zo

an

s

Bila

teria

ns

Eu

meta

zo

an

s

Genes responsible for building animal bodies areshared by virtually every member of the animalkingdom.

These ancient genes are the master control genescalled homeotic genes.

Changes in the regulation of homeotic geneexpression have been significant factors in theevolution of animal diversity.

18.16 EVOLUTION CONNECTION: The genesthat build animal bodies are ancient


Figure 18.16A Figure 18.16B

Antenna

Appendages

1. Describe the defining characteristics of animals.

2. Describe the general animal life cycle and thebasic animal body plan.

3. Describe the Cambrian “explosion” of animaldiversity and two hypotheses that have beenadvanced to explain its occurrence.

4. Explain how a hydrostatic skeleton helps ananimal keep its shape and move.

You should now be able to


5. Characterize the nine animal phyla discussed inthis chapter in terms of the following traits:

a. presence or absence of true tissues,

b. no symmetry, radial symmetry, or bilateral symmetry,

c. no coelom, a pseudocoelom, or a true coelom, and

d. protostomes or deuterostomes.

6. Describe the characteristics of and distinguishbetween each of the following phyla: Porifera,Cnidaria, Platyhelminthes, Nematoda, Mollusca,Annelida, Arthropoda, Echinodermata, andChordata.



7. Define segmentation, explain its functions, andnote the animal phyla where it occurs.

8. Compare the characteristics of the four majorarthropod lineages.

9. Describe the common characteristics of insects.

10. Compare the phylogenetic relationships in Figures18.4 and 18.15, noting similarities and differences.

11. Explain what we have learned about the evolutionof life from the study of “evo-devo.”



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18.1 What is an animal? - Staff Web Sites @ BBHCSDstaff.bbhcsd.org/gardnere/files/2013/02/Chapter-18-Student-Notes.pdf · Chapter 18 The Evolution of ... – presence of true tissues,