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© 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
© 2012 Pearson Education, Inc.
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?
© 2012 Pearson Education, Inc.
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.
18.1 What is an animal?
© 2012 Pearson Education, Inc.
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.
18.1 What is an animal?
© 2012 Pearson Education, Inc.
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.
18.1 What is an animal?
© 2012 Pearson Education, Inc.
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
© 2012 Pearson Education, Inc.
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
© 2012 Pearson Education, Inc.
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”
© 2012 Pearson Education, Inc.
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.
18.3 Animals can be characterized by basicfeatures of their “body plan”
© 2012 Pearson Education, Inc.
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.
18.3 Animals can be characterized by basicfeatures of their “body plan”
© 2012 Pearson Education, Inc.
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.
18.3 Animals can be characterized by basicfeatures of their “body plan”
© 2012 Pearson Education, Inc.
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.
18.3 Animals can be characterized by basicfeatures of their “body plan”
© 2012 Pearson Education, Inc.
Figure 18.3B
Coelom
Body covering(from ectoderm)
Tissue layerlining coelomand suspendinginternal organs(from mesoderm)
Digestive tract(from endoderm)
Figure 18.3C
Body covering(from ectoderm)
Muscle layer(from mesoderm)
Digestive tract(from endoderm)
Pseudocoelom
Figure 18.3D
Body covering(from ectoderm)
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
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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
© 2012 Pearson Education, Inc.
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
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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
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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.
18.5 Sponges have a relatively simple, porous body
© 2012 Pearson Education, Inc.
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.
18.5 Sponges have a relatively simple, porous body
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Adult sponges are sessile and cannot escape frompredators. They deter pathogens, parasites, andpredators by producing
– defensive toxins and
– antibiotics.
18.5 Sponges have a relatively simple, porous body
© 2012 Pearson Education, Inc.
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
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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.
18.6 Cnidarians are radial animals with tentaclesand stinging cells
© 2012 Pearson Education, Inc.
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.
18.6 Cnidarians are radial animals with tentaclesand stinging cells
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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
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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.
18.7 Flatworms are the simplest bilateral animals
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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.
18.7 Flatworms are the simplest bilateral animals
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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
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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
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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
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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.
18.9 Diverse molluscs are variations on a commonbody plan
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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.
18.9 Diverse molluscs are variations on a commonbody plan
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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.
18.9 Diverse molluscs are variations on a commonbody plan
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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
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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.
18.10 Annelids are segmented worms
© 2012 Pearson Education, Inc.
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.
18.10 Annelids are segmented worms
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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
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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.
18.11 Arthropods are segmented animals withjointed appendages and an exoskeleton
© 2012 Pearson Education, Inc.
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.
18.11 Arthropods are segmented animals withjointed appendages and an exoskeleton
© 2012 Pearson Education, Inc.
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.
18.11 Arthropods are segmented animals withjointed appendages and an exoskeleton
© 2012 Pearson Education, Inc.
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.
18.11 Arthropods are segmented animals withjointed appendages and an exoskeleton
© 2012 Pearson Education, Inc.
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
© 2012 Pearson Education, Inc.
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.
18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals
© 2012 Pearson Education, Inc.
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.
18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals
© 2012 Pearson Education, Inc.
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.
18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals
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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).
18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals
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Insects have three pairs of legs, which are adaptedfor
– walking,
– jumping,
– grasping prey,
– digging in soil, or
– paddling on water.
18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals
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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.
18.12 EVOLUTION CONNECTION: Insects arethe most successful group of animals
© 2012 Pearson Education, Inc.
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
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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
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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
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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
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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
© 2012 Pearson Education, Inc.
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
© 2012 Pearson Education, Inc.
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
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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
© 2012 Pearson Education, Inc.
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.
You should now be able to
© 2012 Pearson Education, Inc.
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.”
You should now be able to
© 2012 Pearson Education, Inc.