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Chapter 18
The Evolution of
Animal Diversity
18.5,18.6,18.7,18.10,
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
18.9,18.11
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
What Am I?
• ~1.5 million species known to science
– Over two-thirds are animals!
• Humans have a long-studied animal diversity
– classifying an animal isn’t always easy…
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• Imagine you were the first person to encounter
the animal pictured here
– With all of its varying characteristics, what
would you think it is?
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• Biologists often encounter classification
problems
– When evolution creates organisms with
similar characteristics
A Tasmanian tiger, 1928
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ANIMAL EVOLUTION AND DIVERSITY
18.1 What is an animal?
• eukaryotic, multicellular heterotrophs
– ingest their food
Figure 18.1A
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http://media.pearsoncmg.com/bc/bc_campbell_e
ssentials_3/discvids/_html/index.htm?info_text=c
c5_invertebrates
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INVERTEBRATES
18.5 Sponges - relatively simple, porous body
• Phylum
– Porifera
– simplest animals; no true tissues
Figure 18.5A–C
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• Flagellated choanocytes
– Filter food from the water passing through
the porous body
Pores
Choanocyte
Amoebocyte
Skeletal
fiber
Central
cavity
Figure 18.5D
Choanocyte
in contact
with an
amoebocyte
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Water
flow
Flagella
18.6 Cnidarians - radial animals w/tentacles &
stinging cells
• Phylum
– Cnidaria
– true tissues; radial symmetry
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• 2 body forms:
– Polyps, such as hydra
– Medusae, the jellies
Figure
18.6A–C
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• gastrovascular cavity
– & cnidocytes on tentacles that sting prey
Capsule
(nematocyst)
Coiled
thread
Tentacle
“Trigger”
Discharge
of thread
Prey
Cnidocyte
Figure 18.6D
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18.7 Flatworms = simplest bilateral animals
• Phylum
– Platyhelminthes
– bilateral animals w/no body cavity
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• A planarian’s gastrovascular cavity & simple
nervous system
Gastrovascular
cavity
Nerve cords
Mouth
Eyespots
Nervous
tissue
clusters
Figure 18.7A
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Bilateral symmetry
• Flukes & tapeworms
– parasitic flatworms,
complex life cycles
Figure 18.7B
Colorized SEM 80
Units with
reproductive
structures
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Hooks
Sucker
Scolex
(anterior
end)
18.9 Phylum??
•
Mollusca
•
All have muscular foot & mantle
– may secrete shell that encloses visceral mass
•
Many feed with a “rasping radula”
Visceral mass
Coelom
Heart
Kidney
Reproductive
organs
Digestive
tract
Shell
Mantle
Digestive tract
Mantle
cavity
Radula
Anus
Radula
Mouth
Gill
Mouth
Foot
Nerve
cords
Figure
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Education, Inc. Publishing as Benjamin Cummings
Class Gastropoda
• largest mollusc group
– snails & slugs
Figure 18.9B, C
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Class Bivalvia
• shells in 2 halves
– clams, oysters, mussels, scallops
Figure 18.9D
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Class Cephalopoda
• adapted to be agile predators
– Squids, octopuses
Figure 18.9E, F
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18.10 segmented worms
• Phylum
• Annelida
– added mobility for swimming & burrowing
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Annelids: Earthworms and Their Relatives
• Earthworms
– Eat their way through soil
– closed circulatory system
Anus
Circular
muscle
Epidermis
Segment
wall
Longitudinal
muscle
Dorsal
vessel
Mucus-secreting
organ
Dorsal Coelom
vessel
Brain
Segment wall
(partition
between
segments)
Excretory
organ
Bristles Intestine
Excretory
organ
Digestive
tract
Nerve cord
Bristles
Ventral vessel
Segment
wall
Blood vessels
Mouth
Figure 18.10A
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Nerve cord
Pumping segmental vessels
Giant
Australian
earthworm
Annelids: Polychaetes
• largest group of annelids
– Search for prey on seafloor or
– live in tubes, filter food particles
Figure 18.10B, C
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Annelids: Leeches
• Most leeches
– Are free-living carnivores, but some suck
blood
Figurer 18.10D
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18.11 segmented animals w/jointed appendages
and exoskeleton
• Phylum?
• arthropoda
Cephalothorax
Antennae
(sensory
reception)
Abdomen
Thorax
Head
Swimming
appendages
Walking legs
Figure 18.11A
Pincer (defense)
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Mouthparts (feeding)
Arthropods: Chelicerates
• Horseshoe crabs
Colorized SEM 900
• Arachnids (spiders), scorpions, mites, ticks
A black widow spider (about
1 cm wide)
A scorpion (about 8 cm long)
Figure 18.11B, C
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A dust mite (about 420
µm long)
Arthropods: Millipedes and Centipedes
identified by # of jointed legs per body
segment
Figure 18.11D
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Arthropods: Crustaceans
• nearly all aquatic
– crabs, shrimps, barnacles
Figure 18.11E
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VERTEBRATES
18.15 Derived characters define major clades of chordates
Chordates
Craniates
Vertebrates
Jawed vertebrates
A chordate phylogenetic
tree
Mammals
Reptiles
Amphibians
Lobe-fins
Ray-finned fishes
Sharks, rays
Lampreys
Hagfishes
Tetrapods
Amniotes
Lancelets
– based on a
sequence
of derived
characters
Tunicates
•
Amniotic egg
Legs
Lobed fins
Lungs or lung derivatives
Jaws
Vertebral column
Head
Brain
Figure 18.15
Ancestral chordate
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Milk
ANIMAL PHYLOGENY AND DIVERSITY REVISITED
18.22 phylogenetic tree is work in progress!
Deuterostomes
Arthropods
Nematodes
Annelids
Molluscs
Flatworms
Chordates
Echinoderms
Cnidarians
Sponges
• Molecular-based phylogenetic trees
Ecdysozoans
Lophotrochozoans
Bilaterians
Radial symmetry
Bilateral symmetry
Eumetazoans
True tissues
No true tissues
Figure 18.22
Ancestral
colonial protist
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• Animal development
– May include a blastula, gastrula, and lar val stage
Key
Haploid (n)
Sperm
Diploid (2n)
2
1
Meiosis
Adult
8
Egg
Zygote
(fertilized egg)
3
Eight-cell stage
Metamorphosis
4
Blastula
(cross section)
Digestive tract
Ectoderm
Larva
7
Endoderm
Figure 18.1B
Internal sac
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5
Early gastrula
(cross section)
6
Future
Later gastrula mesoderm
(cross section)
18.2 The ancestor of animals was probably a
colonial, flagellated protist
• Cells in these protists
– Gradually became more specialized and
layered
Somatic
cells
Digestive
cavity
Reproductive
cells
1
Colonial protist,
an aggregate
of identical cells
2
Hollow sphere
of unspecialized
cells (shown in
cross section)
3
Beginning of cell
specialization
(cross section)
Figure 18.2A
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4
Infolding
(cross section)
5
Gastrula-like
“proto-animal”
(cross section)
• Animal diversity
– Exploded during the Cambrian period
Figure 18.2B
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18.3 Animals can be characterized by basic
features of their “body plan”
• Animal body plans
– May vary in symmetry
Top
Dorsal surface
Anterior
end
Posterior
end
Ventral surface
Figure 18.3A
Bottom
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Tissue-filled region
(from mesoderm)
– Vary in body cavity
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Muscle layer
(from mesoderm)
Digestive tract
(from endoderm)
Pseudocoelom
Coelom
Figure 18.3B–D
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Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
– Development as either protostomes or
deuterostomes
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18.4 The body plans of animals can be used to
build phylogenetic trees
• One hypothesis of animal phylogeny
Deuterostomes
Figure 18.4
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Eumetazoans
True tissues
Ancestral
colonial protist
Nematodes
Arthropods
Annelids
Protostomes
Bilaterians
Bilateral symmetry
Radial symmetry
No true tissues
Molluscs
Flatworms
Chordates
Echinoderms
Cnidarians
Sponges
– Is based on morphological comparisons
18.8 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
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• Many nematodes are free-living
– And others are plant or animal parasites
Muscle tissue
Figure18.8A, B
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LM 350
Mouth
Colorized SEM 400
Trichinella juvenile
18.12 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)
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• Many insects undergo
– Incomplete or complete metamorphosis
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A. Order Orthoptera
• The order orthoptera includes
– Grasshoppers, crickets, katydids, and
locusts
Head
Antenna
Thorax
Abdomen
Forewing
Eye
Figure 18.12A
Mouthparts
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Hindwing
B. Order Odonata
• The order odonata includes
– Dragonflies and damselflies
Figure 18.12B
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C. Order Hemiptera
• The order hemiptera includes
– Bedbugs, plant bugs, stinkbugs, and water
striders
Figure 18.12C
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D. Order Coleoptera
• The order coleoptera includes
– Beetles
Figure 18.12D
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E. Order Lepidoptera
• The order lepidoptera includes
– Moths and butterflies
Figure 18.12E
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F. Order Diptera
• The order Diptera includes
– Flies, fruit flies, houseflies, gnats, and
mosquitoes
Haltere
Figure 18.12F
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G. Order Hymenoptera
• The order hymenoptera includes
– Ants, bees, and wasps
Figure 18.12G
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18.13 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
Tube foot
Spine
Figure 18.13B, C
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• The water vascular system
– Has suction cup–like tube feet used for
respiration and locomotion
Anus
Spines
Stomach
Tube feet
Canals
Figure 18.13A
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18.14 Our own phylum, Chordata, is
distinguished by four features
• Chordates, phylum Chordata have
– A dorsal hollow nerve cord
– A stiff notochord
– Pharyngeal slits
– A muscular post-anal tail
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• The simplest chordates are tunicates and
lancelets
– Marine invertebrates that use their
pharyngeal slits for suspension feeding
Excurrent
siphon
Dorsal, hollow
nerve cord
Post-anal tail
Head
Pharyngeal
slits
Mouth
Notochord
Mouth
Muscle
segments
Notochord
Pharynx
Pharyngeal
slits
Digestive tract
Water exit
Adult
(about 3 cm high)
Larva
Figure 18.14A, B
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Segmental
Anus
muscles
Dorsal,
hollow
nerve cord
Post-anal
tail
• Most chordates are vertebrates
– With a head and a backbone made of
vertebrae
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18.16 Lampreys are vertebrates that lack hinged
jaws
• Lampreys lack hinged jaws and paired fins
Figure 18.16A
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• Most vertebrates have hinged jaws
– Which may have evolved from skeletal
supports of the gill slits
Gill
slits
Skeletal
rods
Skull
Mouth
Figure 18.16B
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18.17 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
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Chondrichthyans
• Chondrichthyans
– Have a flexible skeleton made of cartilage
– Include sharks and rays
Figure 18.17A
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Ray-finned Fishes
• The ray-finned fishes have
– A skeleton reinforced with a hard matrix of
calcium phosphate
– Operculi that move water over the gills
Bony skeleton
– A buoyant swim
bladder
Gills
Operculum
Pectoral fin Heart
Rainbow trout,
a ray-fin
Figure 18.17B
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Dorsal fin
Anal fin
Swim bladder
Pelvic fin
Lobe-fins
• The lobe-fin fishes
– Have muscular fins supported by bones
Figure 18.17C
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18.18 Amphibians were the first
tetrapods—vertebrates with two pairs of limbs
• Amphibians
– Were the first tetrapods with limbs allowing
movement on land
Bones
supporting
gills
Figure 18.18A
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Tetrapod
limb
skeleton
– Include frogs, toads, salamanders, and
caecilians
Figure 18.18B–D
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• Most amphibian embryos and larvae
– Still must develop in water
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18.19 Reptiles are amniotes—tetrapods with a
terrestrially adapted egg
• Terrestrial adaptations of reptiles include
– Waterproof scales
– A shelled, amniotic egg
Figure 18.19A, B
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• Living reptiles other than birds
– Are ectothermic
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• 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
Figure 18.19C
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18.20 Birds are feathered reptiles with
adaptations for flight
• Birds evolved from
– A lineage of small, two-legged dinosaurs
Wing claw
called theropods (like dinosaur)
Teeth
(like dinosaur)
Figure 18.20A
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Long tail with
many vertebrae Feathers
(like dinosaur)
• Birds are reptiles that have
– Wings, feathers, endothermic metabolism,
and many other adaptations related to flight
Figure 18.20B
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• Flight ability is typical of birds
– But there are a few flightless species
Figure 18.20C
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18.21 Mammals are amniotes that have hair and
produce milk
• Mammals are endothermic amniotes with
– Hair, which insulates their bodies
– Mammary glands, which produce milk
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• Monotremes lay eggs
Figure 18.21A
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• The embryos of marsupials and eutherians
– Are nurtured by the placenta within the
uterus
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• Marsupial offspring
– Complete development attached to the
mother’s nipple, usually inside a pouch
Figure 18.21B
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• Eutherians, placental mammals
– Complete development before birth
Figure 18.21C
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CONNECTION
18.23 Humans threaten animal diversity by introducing
non-native species
• Introduced species
– Are threatening Australia’s native animals
Figure 18.23A-D
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