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ANIMAL EVOLUTION AND DIVERSITY
18.1 What is an animal?
• Animals are eukaryotic, multicellular
heterotrophs
– That ingest their food
Figure 18.1A
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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)
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)
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Muscle layer
(from mesoderm)
Digestive tract
(from endoderm)
Pseudocoelom
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Figure 18.3B–D
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– Vary in body
cavity
– 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
Protostomes
Bilaterians
Radial symmetry
Bilateral symmetry
Eumetazoans
No true tissues
Figure 18.4
True tissues
Ancestral
colonial protist
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Nematodes
Arthropods
Annelids
Molluscs
Flatworms
Chordates
Echinoderms
Cnidarians
Sponges
– Is based on morphological comparisons
INVERTEBRATES
18.5 Sponges have a relatively simple, porous body
• Sponges, phylum Porifera
– Are the simplest animals and have 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 are radial animals with tentacles
and stinging cells
• Cnidarians, phylum Cnidaria
– Have true tissues and radial symmetry
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•
•
Their two body forms are
–
Polyps, such as hydra
–
Medusae, the jellies
They have a gastrovascular cavity
–
And cnidocytes on tentacles
that sting prey
Figure 18.6A–C
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18.6 Cnidarians are radial
animals with tentacles and
stinging cells
phylum Cnidaria
Have true tissues and
radial symmetry
18.7 Flatworms are the simplest bilateral animals: phylum Platyhelminthes
Are bilateral animals with no body cavity, and a simple nervous system
Gastrovascular
cavity
Nerve cords
Mouth
Eyespots
Nervous
tissue
clusters
Figure 18.7A
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Bilateral symmetry
Flukes and tapeworms
Are parasitic flatworms
with complex life
cycles
Colorized SEM 80
Units with
reproductive
structures
Hooks
Sucker
Scolex
(anterior
end)
Figure 18.7B
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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 & free living
Muscle tissue
Figure18.8A, B
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LM 350
Mouth
Colorized SEM 400
Trichinella juvenile
18.9 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
Visceral mass
Coelom
Heart
Kidney
Mantle
Reproductive
organs
Digestive
tract
Shell
Digestive tract
Mantle
cavity
Radula
Anus
Gill
Mouth
Foot
Figure 18.9A
Nerve
cords
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Radula
Mouth
Gastropods
• Gastropods are the largest group of molluscs
– And include the snails and slugs
Figure 18.9B, C
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Bivalves
• The bivalves have shells divided into two halves
– And include clams, oysters, mussels, and scallops
Figure 18.9D
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Cephalopods
• Cephalopods are adapted to be agile predators
– And include squids and octopuses
Figure 18.9E, F
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18.10 Annelids are segmented worms
• The segmented bodies of phylum Annelida
– Give them added mobility for swimming
and burrowing
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Earthworms and Their Relatives
• Earthworms
– Eat their way through soil
– Have a 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: Segmented Worms
Polychaetes Form the largest group of annelids
Search for prey on the seafloor or live in tubes and filter food particles
Figure 18.10B, C
Figurer 18.10D
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18.11 Arthropods are segmented animals with
jointed appendages and an exoskeleton
• The diversity and success of arthropods
– Are largely related to their segmentation,
exoskeleton, and jointed appendages
Cephalothorax Abdomen
Antennae
(sensory
reception)
Thorax
Head
Swimming
appendages
Figure 18.11A
Walking legs
Pincer (defense)
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Mouthparts (feeding)
Chelicerates
• Chelicerates include
– Horseshoe crabs
Colorized SEM 900
– Arachnids, such as spiders, scorpions,
mites, and 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)
Millipedes and Centipedes
• Millipedes and centipedes
– Are identified by the number of jointed legs
per body segment
Figure 18.11D
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Crustaceans
• The crustaceans
– Are nearly all aquatic
– Include crabs, shrimps, and barnacles
Figure 18.11E
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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
VERTEBRATES
18.15 Derived
characters define
the major clades of
chordates
Chordates
Craniates
Vertebrates
Jawed vertebrates
Tetrapods
Mammals
Reptiles
Amphibians
Lobe-fins
Ray-finned fishes
Sharks, rays
Lampreys
Hagfishes
Amniotes
Lancelets
Tunicates
A chordate phylogenetic
tree is based on a
sequence
of derived
characters
Amniotic egg
Legs
Lobed fins
Lungs or lung derivatives
Jaws
Vertebral column
Head
Brain
Figure 18.15
Ancestral chordate
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Milk
• 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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ANIMAL PHYLOGENY AND DIVERSITY REVISITED
18.22 An animal phylogenetic tree is a work in
progress
• Molecular-based phylogenetic trees
Deuterostomes
Arthropods
Nematodes
Annelids
Molluscs
Flatworms
Chordates
Echinoderms
Cnidarians
Sponges
– Distinguish two protostome clades: the
lophotrochozoans and the ecdysozoans
Ecdysozoans
Lophotrochozoans
Bilaterians
Radial symmetry
Bilateral symmetry
Eumetazoans
No true tissues
True tissues
Figure 18.22
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Ancestral
colonial protist
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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